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Publication year: 2012 Source: Chemical Physics, Available online 8 February 2012 Ae Ran Lim The NMR spectra and the spin-lattice relaxation times, T1, of theH andCs nuclei in (NH4)2-xCsxZnCl4(x=0, 1, and 2) single crystals were determined by using NMR spectroscopy. We investigated the crystallographic structures of these crystals by determining the NH4and Cs occupation probabilities of the two cationic sites. Our NMR experimental results confirm that in (NH4)2ZnCl4there are two crystallographically inequivalent NH4groups, NH4(1) and NH4(2), occupying the A1and A2sites, and that in Cs2ZnCl4there are two crystallographically inequivalent Cs ions, Cs(1) and Cs(2), occupying the A1and A2sites. Both types of NH4ions and both types of Cs ions are found in mixed NH4CsZnCl4crystals; the occupation rates of the two different sites are 1 and 1 for Cs(1) and Cs(2) respectively, and 1 and 1 for NH4(1) and NH4(2) respectively.
Highlights
? TheH andCs NMR spectra in (NH4)2-xCsxZnCl4(x=0, 1, and 2). ? The spin-lattice relaxation times ofH andCs in (NH4)2-xCsxZnCl4(x=0, 1, and 2). ? The NH4and Cs occupation probabilities of the two cationic sites.
Publication year: 2012 Source: Chemical Physics, Available online 8 February 2012 Ya. Vertsimakha, S. Mamykin, P. Lutsyk Optical and photovoltaic properties were studied for phthalocyanine derivatives: sulfonamide zinc phthalocyanine (ZPS), amine zinc phthalocyanine (ZPN) and amine metal-free phthalocyanine (HPN) thin films and thin-film heterostructructures made of the phthalocyanine derivatives with organic semiconductors - N,N‘-dimethylperylene-tetracarboxylicacid diimide, pentacene, lead phthalocyanine. It was shown that sulphonamide substitution of phthalocyanine molecule practically does not affect the absorption spectra. NH2substitution results in appearance of additional absorbance in long-wave range in comparison to the spectra of ZPS. The behavior can be explained by an increase of molecular aggregation due to more efficient interaction of NH2substituted phthalocyanines. The photovoltaic sensitivity of the phthalocyanine films decreases in following sequence ZPS ? ZPN ? HPN.Thermal deposition of N,N‘-dimethylperylene-tetracarboxylicacid diimide and pentacene on thin films of the phthalocyanine derivatives results in formation of sufficiently high potential barrier at the interface. The highest photosensitivity was observed in the heterostructures with pentacene films.
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Highlights
? Sulphonamide phthalocyanines are soluble and the films can be solution processed. ? Sulphonamide substitution of zinc phthalocyanine does not affect photovoltage in film. ? Amine substitution of phthalocyanines decreases photosensitivity of the material. ? The maximum photosensitivity was observed in the heterostructures with pentacene.
Publication year: 2012 Source: Chemical Physics, Available online 8 February 2012 Jaroslav K?íž, Ji?í Dybal, Emanuel Makrlík, Zde?ka Sedláková Binding interaction of Tl, Cs, LiBr, and CsBrwithmeso-octamethylcalix[4]pyrrole (1) in nitrobenzene-d5was studied usingH,C,Li, andCs NMR spectroscopy and DFT quantum-chemical calculations. Although originally declared as typical anion and ion pair receptor,1is shown to bind fairly strongly Tlcations (equilibrium constantK= 1600±80 molL). The binding of Csis much weaker (K =370±18 molL). Neither of these cations invert the conformation of1. LiBrbinds to1(K =1790±160 molL) forming at least four energetically close complexes without much change in its conformation. CsBrpreparedin situfrom LiBrand the cesium salt of dicarbollyl cobaltate in the presence of1binds strongly to1(K = 103514 ± 4000 molL, logK= 5.015) in spite of the slight competition of Liions. The cooperative binding of Csand Brions is shown, in accord with a recent suggestion in literature, to invert the natural conformation of1, the four NH groups binding to Brby hydrogen bonds and the aromatic rings forming a cup binding the embedded Csby its interaction with the ? electron orbitals.
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Highlights
? Thallium is strongly bound by calixpyrrole as a bare cation. ? The bond of cesium as a bare cation is weak. ? In cooperation with bromide ion, cesium is strongly bound as an ion pair.
Publication year: 2012 Source: Chemical Physics, Available online 8 February 2012 N. Nekrašas, K. Genevi?ius, M. Vili?nas, G. Juška Dependencies of photogenerated charge carrier’s extraction current by linearly increased voltage (photo-CELIV) on the light intensity, absorption coefficient and recombination rate were calculated numerically. The simple method for the determination of reduction factor of the Langevin recombination is presented.According to calculations, the time necessary to reach maximum of the CELIV current transient varies more than 10 times depending on parameters mentioned above. Thus, the latter can cause large errors in the estimation of charge carrier’s mobility, which can be corrected using results of the numerical calculations.Numerically calculated photo-CELIV transients were compared with the experimentally obtained current transient in the blends of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) with regioregular poly(3-hexylthiophene) (RR-P3HT), and PCBM with poly(2-methoxy-5-(3,7-dimethyloctyloxy)-para-phenylenevinylene) (MDMO-PPV).
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Highlights
? The photo-CELIV transients were calculated numerically. ? The determination of reduction factor of the Langevin recombination is presented. ? The correction factor for mobility calculation may vary more than 100 times. ? Proposed correction factor for precise mobility estimation should be used.
Publication year: 2012 Source: Chemical Physics, Available online 8 February 2012 J.M. Dahlström, D. Guénot, K. Klünder, M. Gisselbrecht, J. Mauritsson, ... We study the temporal aspects of laser-assisted extreme ultraviolet (XUV) photoionization using attosecond pulses of harmonic radiation. The aim of this paper is to establish the general form of thephaseof the relevant transition amplitudes and to make the connection with the time-delays that have been recently measured in experiments. We find that the overall phase contains two distinct types of contributions: one is expressed in terms of the phase-shifts of the photoelectron continuum wavefunction while the other is linked to continuum–continuum transitions induced by the infrared (IR) laser probe. Our formalism applies to both kinds of measurements reported so far, namely the ones using attosecond pulse trains of XUV harmonics and the others based on the use of isolated attosecond pulses (streaking). The connection between the phases and the time-delays is established with the help of finite difference approximations to the energy derivatives of the phases. The observed time-delay is a sum of two components: a one-photon Wigner-like delay and anuniversaldelay that originates from the probing process itself.
Graphical abstract
Use of attosecond pulses of XUV radiation and an IR laser probe field to study the temporal aspects of photoionization using time-dependent perturbation theory (here depicted as ”Feynman diagrams”).
Highlights
? We find the phase for laser-assisted XUV ionization transition matrix elements matrix elements (M). ? The phase of M is simply: the sum of the scattering phase of the intermediate continuum state and an universal phase. ? The universal phase is independent of the initial state and it leads to a delay observed in attosecond time-delay experiments.
Publication year: 2012 Source: Chemical Physics, Available online 8 February 2012 Ingo Dreissigacker, Manfred Lein We investigate theoretical models for the lateral width of the electron momentum distribution after recollision-free strong-field ionization of atoms. We review the derivation of the tunneling formula and demonstrate that the pre-exponential factor in the saddle-point approximation cannot be neglected if quantitative results are desired. We calculate the widths for hydrogen as well as argon and neon atoms. We compare to results from the time-dependent Schrödinger equation, and to the experimental results from [Arissian et al., Phys. Rev. Lett. 105, 133002 (2010)].
Graphical abstract
The lateral width of an electron wavepacket emitted by an atom in the process of strong-field ionization is described accurately by a quantitative tunneling formula (QTF).
Highlights
? We investigate the electron momentum distribution after strong-field ionization of atoms. ? A quantitative tunneling formula is derived for the lateral width of the distribution. ? The pre-exponential factor differs from previous tunneling formulas. ? We compare to numerical results for hydrogen and to previous experiments for Ar and Ne. ? Quantitative agreement is found when the correct prefactor is taken into account.
Publication year: 2012 Source: Chemical Physics, Available online 8 February 2012 J. Tamuliene, L.G. Romanova, V.S. Vukstich, A.V. Snegursky Fragmentation of the glycine (C2H5NO2) molecule by low-energy electron impact has been studied both experimentally and theoretically. The main emphasis has been given to the mechanisms of the initial molecule fragment production including formation of the doubly-charged CH2NHCOfragment. A special attention has been paid to the energy characteristics of the ionic fragment yield. The geometrical parameters of the initial molecule rearrangement have also been analyzed.
Graphical abstract
The area of the mass-spectrum of the glycine molecules showing the doubly-charged CH2NHCOfragment production.
Highlights
? We measure glycine molecule mass spectrum. ? The appearance energies for positively charged fragment ions are determined. ? We suggest the most energetically beneficial dissociation channels. ? Production of the doubly-charged fragment is observed.
Publication year: 2012 Source: Chemical Physics Letters, Available online 9 February 2012 Kayo Suda, Masahide Terazima, Yoshifumi Kimura Excitation wavelength dependence of photo-induced intramolecular excited state proton transfer reaction of 4’-N,N-diethylamino-3-hydroxyflavone in various liquids has been investigated by steady-state and time-resolved fluorescence measurements. It was found that the relative fluorescence intensity of the tautomer excited state to that of the normal excited state significantly decreases in ionic liquids with changing the excitation wavelength from 380nm to 470nm. The initial proton transfer rate excited at 470 nm was different from that obtained at 400 nm excitation. The excitation wavelength dependence was discussed in relation with the inhomogeneous distribution of the solute in the ionic liquids.
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Highlights
? Excited state intramolecular proton transfer (ESIPT) was measured by fluorescence. ? The reactant was 4’-N,N-diethylamino-3-hydroxyflavone. ? The ESIPT was investigated at different excitation wavelength. ? The yield of ESIPT in ionic liquids was significantly modified. ? The PT rate was also revealed to be dependent on the excitation wavelength.
Publication year: 2012 Source: Chemical Physics Letters, Available online 8 February 2012 G. Krishna Podagatlapalli, Syed Hamad, S. Sreedhar, Surya P. Tewari, S. Venugopal Rao In this communication we report the fabrication of nanoparticles (NPs) and nanostructures through the interaction of ultrashort laser pulses (?40 fs) with bulk Aluminum immersed in chloroform and carbon tetrachloride. The size distribution and surface morphology of substrates were investigated using scanning electron microscope images. Depending on the focal position we observed sub-micron structures and nano-ripples on the irradiated surface. Picosecond nonlinear optical studies of the prepared NPs colloidal solutions using open aperture Z-scan technique demonstrated complex behavior of switching from saturable absorption to reverse saturable absorption (RSA) at lower peak intensities to pure RSA at higher peak intensities.
Graphical abstract
Characterization of Al nanoparticles obtained using femtosecond ablation. (a) distribution histogram in colloidal CCl4solution, (b) UV-Vis extinction spectra of the prepared colloidal solution, (c) Open aperture Z-scan curves obtained for colloidal CCl4at three different intensities in increasing fashion (from green to red) in picosecond regime. SEM image of Al NPs in CCl4is shown in the central figure.
Highlights
? We generated well dispersed Al nanoparticles with less oxide cladding through fs laser ablation. ? We observed micro- and nano-structure formation on the substrate with different focusing conditions. ? We could explain effect of polarity of the liquid medium on the size of nanoparticles formed. ? Nonlinear optical properties of the colloidal solutions of nanoparticles were carried out.
Publication year: 2012 Source: Chemical Physics Letters, Available online 8 February 2012 A. Lepore, S. Baccaro, C. Casieri, A. Cemmi, F. De Luca NMR correlation maps of paper samples suggest a two-site residence model for water in the ultrastructure of cellulose. When cross-linking and degradation of cellulose occur due to?-irradiation-induced ageing, a significant fraction of water appears confined into low-mobility sites of the cellulose matrix. As the cellulose damage grows more pronounced, the two-site structure turns into a single-site water arrangement.
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Highlights
? NMR 2D technique for studying ageing effect on Whatman paper. ? NMR 2D is able to detected gamma irradiation effect: crosslinking and degradation. ? Experimental results suggest two-site residence model for water siting in cellulose. ? The two-site collapse in one site with increasing of absorbed doses.
Publication year: 2012 Source: Chemical Physics Letters, Available online 8 February 2012 Wei Xu, Xiangdong Meng, Wenyu Ji, Pengtao Jing, Jinju Zheng, ... Optical properties of Mn-doped ZnxCd1-xS nanocrystals were studied by steady-state and time-resolved photoluminescence (PL) spectroscopy. The doped nanocrystals with PL quantum yield up to 29% were synthesized by growing a thin ZnS layer on the MnS core and then growing a CdS layer with different thicknesses using nucleation-doping strategy. The absorption band edge of ZnxCd1-xS nanocrystals was tuned from 425 nm to 475 nm by growing the CdS layer with various thicknesses under different Zn/Cd molar ratios to vary the composition. The PL band of Mn-doped nanocrystals was found to originate from emissions of Mnions and defect states.
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Highlights
? Optical properties of Mn-doped ZnxCd1-xS NCs were studied. ?The NCs with PL QY up to 29% were synthesized based on MnS/ZnS/CdS structure. ? The composition was controlled by growing various thicknesses CdS layer. ? The PL band of NCs was composed by the emissions of Mnions and defect states.
Publication year: 2012 Source: Chemical Physics Letters, Available online 8 February 2012 Taejin Kim, Rajeev S. Assary, Christopher L. Marshall, David J. Gosztola, Larry A. Curtiss, ... A combination of Raman spectroscopy and density functional methods was employed to investigate the spectral features of selected molecules: furfural, 5-hydroxymethyl furfural (HMF), methanol, acetone, acetic acid, and levulinic acid. The computed spectra and measured spectra are in excellent agreement, consistent with previous studies. Using the combination and prediction spectrum method (CPSM), we were able to predict the important spectral features of two platform chemicals, HMF and levulinic acid. The results have shown that CPSM is a useful alternative method for predicting vibrational spectra of complex molecules in the biomass transformation process.
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Highlights
? Derived Raman spectra of cyclic and acyclic organic chemicals. ? Theoretically calculated vibrational wavenumbers with the B3LYP method using the 6-31+G(2df,p) basis set. ? Applied the combination and prediction spectrum method (CPSM) to hydroxymethyl furfural and levulinic acid. ? Demonstrated that CPSM is a feasible method for predicting vibrational spectra of complex molecules.
Publication year: 2012 Source: Chemical Physics Letters, Available online 9 February 2012 Michele Folmar, Tanya Shtoyko, Rafal Fudala, Irina Akopova, Zygmunt Gryczynski, ... In this report we discuss the plasmonic scattering and fluorescence enhancement properties of silver triangular nanoprisms synthesized by a chemical reduction method. Plasmonic platforms (PPs) were made by air-dried self-assembly of the silver triangular nanoprisms onto a gold mirror. Fluorescence enhancement was investigated using methyl-azadioxatriangulenium chloride (Me-ADOTA·Cl) dye in PVA deposited on PPs. Confocal microscopy results showed a 15-fold enhancement of the dye overall, with over 50-fold enhancements on ‘hot spot’ regions. The presence of silver nanoprisms significantly reduced the lifetime of the fluorophore. The preparation of silver triangular nanoprismsand observed emission data are highly reproducible.
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Highlights
? Silver triangular nanoprismswere prepared and used to make plasmonic platforms. ? Over 50-fold enhancements on ‘hot spot’ regions were measured. ? Silver nanoprisms significantly reduced the lifetime of the fluorophore.
Publication year: 2012 Source: Chemical Physics Letters, Available online 9 February 2012 V.M. Gun’ko, V.V. Turov, A.V. Turov Interactions of 30% aqueous solution of H2O2with nanosilica (409 m/g) in CCl4or CD3Cl media with addition of CD3CN or (CD3)2SO were studied usingH NMR spectroscopy and quantum chemistry methods. In nonpolar medium, two types of structures are formed with strongly associated water (?H= 4-6 ppm) including different amounts of H2O2. H2O/H2O2bound to silica in weakly polar CD3Cl with addition of CD3CN or DMSO form three types of clusters with: (i) concentrated H2O2at ?H= 9-11 ppm; (ii) concentrated water and dissolved co-solvents; and (iii) organic solvents containing certain amounts of water and H2O2.
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Highlights
? Aqueous solution of H2O2is clustered at a nanosilica surface. ? Nonpolar and weakly polar dispersion media affects clustered structure of H2O2/H2O. ? Small addition of a polar solvent strongly change both H2O2and H2O structure.
Publication year: 2012 Source: Chemical Physics Letters, Available online 8 February 2012 Christian Braun, Sebastian Proch, Hyun Ook Seo, Young Dok Kim, Gerd Ganteför Relaxation dynamics of optically excited states of Au3and Au3(H2O)mwere studied via femtosecond time-resolved photoelectron spectroscopy (fsTRPES). Au3exhibits photo-dissociation into either (Au2+ Au1) or (Au2+ Au1) with a time constant of 1.6 ns. One water molecule adsorbed on Au3opened new photo-induced dissociation channels with a much shorter time constant. More than one water molecules on Au3inhibited photo-dissociation, most likely as a result of facile dissipation of excess energy of optically excited states by nuclear motions of clusters. Photochemical path can be controlled by adjusting the number of water molecules interacting with the ionic species.
Graphical abstract
SDFSDFSD
Highlights
? Relaxation dynamics of optically excited states of Au3and Au3(H2O)mwere studied. ? One water molecule adsorbed on Au3opened new photo-dissociation channels. ? More than one water molecules on Au3inhibited photo-dissociation. ? Photochemistry is controlled by adjusting the number of adsorbed water molecules.
Publication year: 2012 Source: Chemical Physics Letters, Available online 7 February 2012 R. Mével, P.A. Boettcher, J.E. Shepherd The present study reports gas phase absorption cross sections at 3.39?m of 21 liquid hydrocarbons. Measurements were performed in the temperature range 303-413 K using an infrared He-Ne laser. In addition to n-alkanes, a number of cyclo-alkane, aromatic, and substituted hydrocarbons were investigated. The results demonstrate that (i) the absorption cross sections are temperature independent in the studied range, and that (ii) the aromatic and substituted hydrocarbons exhibit much smaller cross sections than n-alkanes for an identical number of C-H bonds. A tentative empirical correlation has been developed and shown to accurately predicts the cross section.
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Highlights
? The cross sections at 3.39?m of 21 liquid hydrocarbons have been measured. ? Measurements have been made for alkanes, aromatics and substituted hydrocarbons. ? An empirical correlation has been developed and predicts accurately the cross section.
Publication year: 2012 Source: Chemical Physics Letters, Available online 7 February 2012 Takahiro Ohkubo, Mallory Gobet, Vincent Sarou-Kanian, Catherine Bessada, Muneharu Nozawa, ... Lithium diffusion was measured inxLi2O–(1-x)B2O3 melts as a function of temperature and composition by high-temperature pulsed field gradient NMR. TheLi self-diffusion coefficients were found to increase with increasingwhen compared at the same temperature. It was of much interest thatin the moltenxLi2O–(1-x)B2O3 system decreased monotonously with increasing Li2O content up toand then increased atand 0.5.
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Highlights
? We examined lithium diffusion in Li2O-(1-x)B2O3 melts by high-temperature PFG NMR. ? Activation energy, Ea, were compared with viscosity, density and MD simulations. ? Ea had the minimum value at x=0.4, which was the same as density and BO4 fraction. ? We concluded Ea depends on the depolymerization network and Coulomb interaction.
Publication year: 2012 Source: Chemical Physics Letters, Available online 8 February 2012 Li-Hua Gan, Qing Chang, Li Xu, Xing-Liang Huang, Chun-Ying Shu, ... Classical isomers of fullerenes usually obey the pentagon adjacent penalty rule. However, density functional theory calculations demonstrate that an isomer of fullerene C60with 15 pentagon-pentagon fusions is lower in energy that any isomer of C60with 14 pentagon-pentagon fusions and thus violates the established pentagon adjacent penalty rule. Further examination demonstrates that this isomer follows the spherical rule; however it is anti-aromatic with positive nucleus-independent chemical shifts at the cage center and most ring centers. The calculations show that hydrogenation and cluster encapsulation are both highly exothermic and demonstrate that this isomer may be captured in the form of its derivatives.
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Highlights
? The isomer of fullerene C60-288 violates the established pentagon adjacent penalty rule. ? The fullerene C60-288 is anti-aromatic. ? The fullerene C60-288 may be captured in the form of its derivatives.
Publication year: 2012 Source: Chemical Physics Letters, Available online 8 February 2012 Seda Surucu, Sinan Akpinar Quantum scattering dynamics calculation is used to study initial-state-resolved reaction probabilities, integral cross section, initial state selected reaction rate constants and thermal rate constant for both channels of the reactionND(a?) + H(S) ? productson the modified NH2potential energy surface (PES) using centrifugal sudden (CS) approximation. This surface is barrierless and therefore, for depletion channel, probabilities have small centrifugal thresholds and present sharp and large resonances, associated with long-lived collision complexes. Integral cross sections for both reactions depend strongly on initial rotational states. In particular, thermal reaction rate constant for depletion channel is in good agreement with experimental and semiclassical results.
Highlights
? Quantum dynamics of astrophysically important H+ND reaction is studied. ? Integral reaction cross sections and thermal rate constants are reported. ? The depletion reaction rate is higher than exchange reaction rate. ? The sole reactivity is governed by the depletion channel at higherJvalue.
Publication year: 2012 Source: Chemical Physics Letters, Available online 9 February 2012 Guo-xun Wu, Qing-yuan Meng, Yu-hang Jing Using the non-equilibrium Green’s function method together with the density-functional theory, the electronic transport properties of various junction models constructed from different graphene nanoribbon (GNR) units via topological defects have been evaluated. It is found that the armchair-zigzag GNR (A-Z GNR) junctions can display the diode-like behavior. Various ring structures at the interface show different effects on the transport properties and conductivity of the junctions. The simulation results suggest that the proposed models are promising for future applications in novel nano-electronics and molecular devices.
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Highlights
? We model GNR-GNR junctions with topological defects and discuss the geometry. ? We discuss the diode behavior of the junctions. ? The 5-7-5 ring structure is regarded as the most superior defect for the diode behavior and conductivity. ? Increasing of width of the GNR will decrease the diode behavior. ? Geometry affect the conductivity of the junction obivously.
Publication year: 2012 Source: Chemical Physics Letters, Available online 6 February 2012 Tomáš Man?al, František Šanda Generalized master equations valid for the third order response of an optically driven multi-level electronic system are derived within Zwanzig projection formalism. Each of three time intervals of the response function is found to require specific master equation and projection operator. Exact cumulant response functions for the harmonic profiles of the potential energy surfaces leading to Gaussian spectral diffusion are reproduced. The proposed method accounts for the nonequilibrium state of bath at the border of intervals, and can be used to improve calculations of ultrafast non-linear spectra of energy transferring systems.
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Highlights
? We consider non-linear response functions for a simple two-level molecular system. ? It is shown that it cannot be constructed using a single reduced density matrix master equation. ? A set of master equations is derived which together reproduce the two-level response function. ? Parametric projection operators are introduced to derive proper equations in general cases.
Publication year: 2012 Source: Chemical Physics Letters, Available online 7 February 2012 Huyen Thi Nguyen, Thuc-Quyen Nguyen, Minh Tho Nguyen The molecular structures, electronic and charge-transport properties of three conjugated polyelectrolytes (CPEs) including PFPhCO2Na, PFPhSO3Na, and PFPhBIm4 are studied using the density functional theory with B3LYP functional. The charge injection and charge transport properties are investigated through the ionization energies, electron affinities, lowest allowed excitation energies, reorganization energies and electron transfer integrals. The electron/hole injections have great effect on the planarity of cationic/anionic CPEs. The band gaps of the CPEs do not vary significantly with the charged groups and counterions. Charge-transport properties show that the PFPhSO3Na and PFPhBIm4 are good candidates for electron-transport materials.
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Highlights
? In conjugated polyelectrolytes (CPEs), electron and hole injections vary the planarity of the monomers. ? Their band gaps are invariant for monomers bearing the same backbone. ? CPEs could be potential candidates for electron-transport materials.
Publication year: 2012 Source: Chemical Physics Letters, Available online 7 February 2012 Antonio Bauzá, David Quiñonero, Pere M. Deyà, Antonio Frontera Complexes of anions with several six-membered inorganic rings with more or less aromatic character have been optimized at the RI-MP2/aug-cc-pVDZ level of theory. The rings studied are hexazine (N6), boroxine (B3O3H3), borazine (B3N3H6), 1,3,5,2,4,6-triazatriborinine (B3N3) ring, and borthiin (B3S3H3). The anion–? complexes are energetically favorable and the interaction has been characterized by means of the Bader’s theory of “atoms-in-molecules” and partitioning the energy using the SAPT method. Experimental evidence of the importance of this interaction in some inorganic rings has been obtained from the Cambridge Structural Database.
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Highlights
? Energetic and geometric features of unprecedented anion–? complexes involving inorganic rings at the RI-MP2/aug-cc-pVDZ. ? Molecular Electrostatic Potential Surfaces of five six-membered inorganic rings. ? Partitioning of the interaction energy using DFT-SAPT. ? Experimental evidences from the CSD database.
Publication year: 2012 Source: Chemical Physics, Available online 6 February 2012 Andrei N. Salak, João Tedim, Alena I. Kuznetsova, José L. Ribeiro, Luís G. Vieira, ... Zn-Al layered double hydroxides (LDH) are promising as nanocontainers of corrosion inhibitors in self-healing corrosion protection coatings. Zn(2)Al-vanadate (Zn/Al=2:1) is prepared by anion exchange from the parent composition Zn(2)Al-nitrate at pH?8. Crystal structure and vibrational spectra of both LDHs have been studied in comparison. Their interlayer distances are rather larger than those corresponding to the most compact arrangement of the intercalated anions. Nevertheless, no sign of a turbostratic disorder has been detected in these LDH. Based on the analysis of the spectroscopic data in combination with the XRD results, it has been shown that vanadate anion, which substitutes nitrate at the anion exchange, is pyrovanadate,. The observed disorder in the hydroxide layers in Zn(2)Al-V2O7is likely to result from strong interactions between Vand Zn/Al. Although Zn(2)Al-NO3is less disordered than Zn(2)Al-V2O7, it exhibits no long-range order in arrangement of cations in the hydroxide layers.
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Highlights
? Vanadate anion, which substitutes nitrate in Zn(2)Al layered hydroxide, is. ? Site symmetry of nitrate in Zn(2)Al-NO3is lower than D3hand likely to be C2?. ? Disorder in Zn(2)Al-V2O7results from interactions between Vand Zn/Al.
Publication year: 2012 Source: Chemical Physics Letters, Available online 6 February 2012 M. Lino da Silva, J. Loureiro, V. Guerra The Forced Harmonic Oscillator (FHO) model is applied to the production of a multiquantum dataset of V–T and V–D rates for O2–O2collisions, for T=100–100,000K. A simplified 1D O2–O2intermolecular potential, accounting for long-range interactions, has been obtained through comparison of FHO and reference state-specific rates. A Morse potential with parametersand E=380K provides the best fit between those. This potential has then been applied to the production of the overall multiquantum V–T and V–D rates, considering 47 vibrational levels. The resulting thermal dissociation rates agree remarkably well with experimental dissociation rates.
Highlights
? The internuclear Morse potential for O2-O2collisions has the parametersandE = 380K. ? The O2molecule has 47 vibrational levels. ? The FHO approach provides rates which compare well with reference rates for O2-O2. ? A full dataset of V-T and V-D rates for O2-O2collisions has been produced. ? Experimental thermal dissociation rates are very well reproduced by this dataset.
Publication year: 2012 Source: Chemical Physics, Available online 3 February 2012 M. Karbowiak, P. Gnutek, C. Rudowicz Crystal field (CF) analysis of energy levels for Ndand Erions in LaAlO3, YAlO3, and LaGaO3single crystals is presented. It is shown that a combined approach comprising the ascent/descent in symmetry (ADS) method combined with superposition model (SPM) analysis can be successfully used for analysis of low-symmetry systems. The present ADS/SPM approach is less labour and time consuming as compared, e.g., with Monte-Carlo method and it also allows maintaining the relationship between the crystallographic axis system and the nominal axis systems of fitted CFP sets. For orthogallates and orthoaluminates the actual Cssymmetry, resulting from distortion of perovskite structure, may be successfully approximated for both systems by the ADS chain C4v? C3(D3) ? Csor C3(D3) ? Cssymmetry. The possibility of using of approximated symmetries for orthogallates or orthoaluminates can be useful for interpretation of energy levels for this family of compounds of technological importance, particularly in the case when the number of available experimental energy levels is insufficient for full Csparameterization. The novel aspect of the combined ADS/SPM approach is that possible higher symmetry approximations employing also the axis systems oriented differently than for the actual symmetry are searched for, taking advantages of the transformation properties of CF parameters sets.
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Highlights
? CF analysis of energy levels for Ndand Erions in ABO3crystals is presented. ? Combined ADS/SPM strategy is employed. ? Its usefulness for successful analysis of low-symmetry systems is proved. ? Structural relationships between different ion-host systems are emphasized.
Publication year: 2012 Source: Chemical Physics, Available online 3 February 2012 Petro Lutsyk, Krzysztof Janus, Juliusz Sworakowski, Anna Kochalska, Stanislav Nešp?rek The paper reports on kinetic measurements of coloring and bleaching reactions in the spiropyran - merocyanine photochromic system dissolved in poly(methyl methacrylate) matrix (PMMA/SP). The system was earlier used as the gate insulator in a photo-switchable organic field effect transistor (OFET), and the switching was attributed to the photochromic reaction taking place in the polymer matrix. The present measurements aimed at elucidating the mechanism of the switching by comparing the rate constants of the coloring and bleaching reactions with the rate constants of processes responsible for capacitance changes. The comparison of the rate constants seems to confirm the role of the photochromic process: to within experimental uncertainty the rate constants determined from the two methods are similar. Measurements of the temporal evolution of absorbance additionally reveal existence of an irreversible fatigue reaction, probably associated with admission of oxygen to some samples. The presence of oxygen is also responsible for a deterioration of performance of the OFETs under study.
Graphical abstract
Upper left: Architecture of the OFETs under studyLower left: Photochromic reaction in the spiropyran-merocyanine systemRight: Changes of capacitance due to the photochromic reaction taking place in PMMA film containing dissolved spiropyran
Highlights
? Reaction in a photochromic system changes electric permittivity of a polymer film. ? Time dependences of UV/VIS spectra and electric permittivity were measured. ? Coloring and fading rate constants determined from both methods are similar. ? The photoactive polymer film was used as gate insulator in photoswitchable OFETs. ? Admission of oxygen results in an irreversible reaction of the photochromic system..
Publication year: 2012 Source: Chemical Physics Letters, Available online 3 February 2012 Paulo A. Nogueira, Hamilton Varela, Roberto B. Faria Herein we present results on the oscillatory dynamics in the bromate-oxalic acid-acetone-Ce(III)/Ce(IV) system in batch and also in a CSTR. We show that Ce(III) is the necessary reactant to allow the emergence of oscillations. In batch, oscillations occur with Ce(III) and also with Ce(IV), but no induction period is observed with Ce(III). In a CSTR, no oscillations were found using a freshly prepared Ce(IV), but only when the cerium-containing solution was aged, allowing partial conversion of Ce(IV) to Ce(III) by reaction with acetone.
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? No oscillations are observed in a CSTR on the bromate-oxalic acid-acetone-Ce(IV) system. ? Ce(III) is the only catalyst necessary to produce oscillations on this system. ? When Ce(IV) is used, the induction period is a time necessary to convert Ce(III) to Ce(IV).
Publication year: 2012 Source: Chemical Physics Letters, Available online 3 February 2012 K. Didriche, C. Lauzin, T. Földes CW-cavity ring down spectroscopy was used to record the spectrum ofC2H2-N2in a free jet expansion around the 2CH acetylene band. 20 lines were assigned thanks to combination differences, which were combined with literature values leading to the retrieval of ground state rotational constants consistent for a broader set ofJ”. Effective rotational constants, the band origin and the estimation of the lifetime of the perturbed upper state are determined.
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? CRDS spectrum of C2H2-N2was recorded around the 2CH acetylene band. ? 20 lines are assigned thanks to combination differences. ? Effective rotational constants and the band origin of the upper state are determined. ? Lifetime of the upper state is retrieved.
Publication year: 2012 Source: Chemical Physics Letters, Available online 3 February 2012 Eugene Mamontov Using quasielastic neutron scattering, we compare dynamics in single-element liquids, glass-forming selenium and non glass-forming gallium. There is a single jump-diffusion process in gallium, whereas in selenium there is also a faster, spatially localized process. The fast and slow processes describe ?- and ?-relaxation, respectively. We then analyze an archetypical glass-former, glycerol, to show that the two-component fit, with ?- and ?-relaxations explicitly separated, yields the correct value for the translational diffusion coefficient and provides information on the spatial localization of the ?-relaxation that is not experimentally accessible otherwise.
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? Glass-forming and non glass-forming liquids are studied using quasielastic scattering. ? Glass-formers exhibit two separate relaxation components, non glass-former only one. ? The faster of the two components corresponds to the beta-relaxation process. ? The beta-relaxation can be described as a diffusion process in confined space (cage).
Publication year: 2012 Source: Chemical Physics, Available online 3 February 2012 Katarzyna Piela, Boles?aw Kozankiewicz, Józef Lipi?ski, M. Magdalena Szostak The fluorescence and phosphorescence spectra ofN-benzyl-2-methyl-4-nitroaniline (BNA) orthorhombic crystal were measured between 5 and 200 K. The fluorescence spectrum of BNA in a Shpol’skii matrix ofn-heptane was also recorded at 5 K. The electronic absorption spectra parameters such as singlet and triplet state energies, dipole moments and oscillator strengths were calculated by semi-empirical and TD DFT methods. The calculated energies of singlet and triplet states and electronic transitions in the BNA molecule were compared with the experimental results. The phosphorescence decay time was estimated to be 270 ms at 5 K. It is presumed that the disappearance of vibronic structure above 30 K observed in the fluorescence spectra is caused by the nitro group vibrations while the structured phosphorescence originates from the trap states. The role of molecular shape towards emission processes in BNA crystal in terms of structure-property relationship is discussed.
Graphical abstract
Fluorescence and phosphorescence spectra ofN-benzyl-2-methyl-4-nitroaniline (BNA) crystal at 5 K and charge density at LUMO orbital calculated by TD DFT method.
Highlights
? Temperature dependent fluorescence and phosphorescence spectra of BNA crystal. ? Molecular character of fluorescence in BNA crystal. ? Vibronic structure of fluorescence is attributed to nitro group vibrations. ? Phosphorescence originates from shallow traps depopulated above 30 K. ? Intramolecular charge transfer enhanced byN-benzyl substitution of BNA..
Publication year: 2012 Source: Chemical Physics, Available online 2 February 2012 H. Mineo, Y.H. Wang, S.D. Chao, S.H. Lin We have calculated the vibrational and rotational autoionization rate constants for diatomic molecules H2, N2, and HCl in high Rydberg states by employing the density matrix formulation with the inverse Born-Oppenheimer approximation basis set. The purpose is to simulate the main radiationless processes occurring in zero electron kinetic energy (ZEKE) spectroscopy. The quantum numbers and the energy dependences of the calculated autoionization rate constants are represented as the scaling laws via nonlinear regression. These data provide a suitable starting point for quantitative study of the intricate dynamics involved in ZEKE Rydberg states.
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? Rovibrational autoionization rate constants for diatomic molecules. ? Density matrix formulation based on the model of IBOA. ? Quantum number and energy dependences are studied.
Publication year: 2012 Source: Chemical Physics, Available online 2 February 2012 Christian Gnodtke, Ulf Saalmann, Jan-Michael Rost The photo-electron spectrum resulting from multi-photon absorption of an extended target, such as an atomic cluster or a large molecule, from an intense laser pulse with photon energies larger than the ionization potential of the atomic constituents is discussed. We develop an approximate analytical framework and provide simple analytical expressions for the shape of the photo-electron spectrum in the limit of sequential and parallel ionization, realized by long and short pulses, respectively. The width of the spectrum provides valuable information about the absorbed photons of the target in relation to its extension.
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Sketch of the electrons released upon multi-photon ionization of a cluster. The recorded kinetic-energy spectra of the electrons depend on the duration of the ionizing pulse.
Highlights
? Microscopic calculations of electron spectra as a function of the pulse length. ? Analytical expression for the spectra in the limits of parallel and sequential emission. ? Discussion of the absolute width of the spectra for experimental diagnostics.
Publication year: 2012 Source: Chemical Physics, Available online 3 February 2012 Willian Hermoso, Fernando R. Ornellas All doublet and quartet electronic states correlating with the first dissociation channel of SeCl and some Rydberg states are investigated theoretically at the CASSCF/MRCI level of theory using extended basis sets, including the contribution of spin-orbit effects. The similarity of the potential energy curves with those of SeF suggests that spectroscopic constants for the ground (X?) and the first excited quartet (a?) of SeCl could also be determined via an emission resulting from the reaction of selenium with atomic chlorine. The coupling constant of the ground state atReis estimated as ?1610 cm. The potential energy curves calculated and the derived spectroscopic constants do not support the interpretation and assignment of the scarce transitions recorded experimentally as due to? ?? emissions. That the few observed lines might arise from transitions from the stateto a very high vibrational level of the stateis an open possibility, however, the number of vibrational states and the calculated ?G1/2differ significantly from the reported ones.
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? Characterization of a new molecular species: SeCl. ? High-levelab initiocalculation including spin-orbit effects. ? State-of-art excited states potential energy curves description. ? Accurate electronic and vibrational spectra.
Publication year: 2012 Source: Chemical Physics Letters, Available online 2 February 2012 Toshiki Yamada, Yoshihiro Haruyama, Katsuyuki Kasai, Toshifumi Terui, Shukichi Tanaka, ... We show that by observing SHG interference bR thin films prepared by a simple dip coating technique have a polar orientation with C?symmetry. The SHG interference measurements were performed under various input and output polarization combinations at different incident angles or under the rotation of the quarter-wave retardation plate at specific incident angles. The interference patterns provide us with insight into the characteristics of non-vanishing nonlinear optical coefficients including chiral components. Abundant information can be obtained by observing SHG interference by using two chiral SH active films.
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? bR thin films prepared by a simple dip coating have a polar orientation with C?. ? The interference fringes in p-p and s-p have opposite phase with that in p-s. ? Enhanced or restricted chiral SHG was observed at specific incident angles. ? Abundant information can be obtained by observing SHG interference.
Publication year: 2012 Source: Chemical Physics Letters, Available online 31 January 2012 M.L. Strekalov Rotational time-dependent populations are determined by simulating the experimental data via analytical solution to the master equation considered as a scaling law that is a new data reduction method. The state-to-state rate constants are obtained from a formalism of the theory with the same accuracy as recovered populations.
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Ortho-acetylene in ?2= 1 at 155 K. Evolution of the measured (dots) and predicted (line) rotational population forj = 7 after excitation ofji = 9.
Highlights
? An analytical solution to the master equation is obtained. ? A new scaling law for evaluation of rotational populations is derived. ? This is a new data reduction method. ? Populations are then determined by simulating experimental data by the scaling law.
Publication year: 2012 Source: Chemical Physics Letters, Available online 2 February 2012 Changqing Cheng, Satish S.T. Bukkapatnam, Lionel M. Raff, Martin Hagan, Ranga Komanduri The computation time for Monte Carlo (MC) simulation of a nanostructure growth process was shown to be reduced by an order of magnitude compared to conventional atomistic and meso-scale models through the prediction of the structure evolution ahead of every growth step. This approach used to grow of one of the longest (?194 nm) reported carbon nanotubes (CNTs) from atomistic simulations. The key to the approach is the finding from simulation experiments that the CNT synthesis process exhibits nonlinear and recurring near-stationary dynamics
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? One of the longest CNTs (194 nm) from simulations. ? Simulation time reduced from about from 3–4 weeks to 2–5 days. ? CNT growth found to exhibit distinct nonlinear and nonstationary dynamics. ? Generic growth prediction approach to accelerate nanosynthesis simulations. ? Accurately captures and explains trends observed in physical experiments.
Publication year: 2012 Source: Chemical Physics Letters, Available online 2 February 2012 Daniel A. Lovey, Rodolfo H. Romero We discuss the general form of the transmission spectrum through a molecular junction in terms of the Green function of the isolated molecule. By introducing a tight binding method, we are able to translate the Green function properties into practical graphical rules for assessing beforehand the possible existence of antiresonances in an energy range for a given choice of connecting sites. The analysis is exemplified with a benzene molecule under a hypothetical local gate, which allows one to continuously tune the on-site energy of single atoms, for various connection topologies and gate positions.
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? We discuss properties of the transmission function of single molecule junctions. ? Analysis of transmission antiresonances from Hückel molecular orbitals. ? Effect of application of gate potentials on aromatic molecules. ? Discussion of interplay between gate position and topology of connections.
Publication year: 2012 Source: Chemical Physics Letters, Available online 2 February 2012 Yanhui Lou, Zhaokui Wang, Shigeki Naka, Hiroyuki Okada The authors investigate the effects of metal work functions on charge transport characteristics in P3HT: PCBM bulk heterojunction under illumination by evaluating the temperature dependence of current-voltage characteristics. Schottky thermal emission current plays a dominant role on charge transport in the devices with Au or Al alloys used as electrodes. Whereas, a combined bulk limited conduction mechanism corresponding to three-dimensional variable-range hopping model and space charge limited current (SCLC) with an exponential distribution of traps (filled and unfilled) occurs in the device with Al used as electrode. And a shift to LUMO state of PCBM for trap density distribution is observed due to temperature dependence of Fermi level in PCBM material.
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? Carrier transport property in P3HT: PCBM blend is investigated under illumination. ? Schottky thermal emission current is dominant in devices using Au or AlLi as electrode. ? SCLC with traps (filled and unfilled) is observed in devices using Al as electrode. ? The bulk trap density in P3HT: PCBM blend is evaluated by differential method.
Publication year: 2012 Source: Chemical Physics Letters, Available online 2 February 2012 Neal D. Kline, Terry A. Miller The near infrared-electronic absorption spectrum of the 2,1-hydroxypropyl peroxy radical (2,1-HPP) has been recorded at room temperature by cavity ringdown spectroscopy. Twenty-five conformers of 2,1-HPP are predicted to exist as minima on the potential energy surface calculatedviaeitherab initioor density functional theory. However, the experimental spectrum is explained in terms of the origin bands and vibrational structure of the three conformers predicted to be most stable. In addition to the OO stretch and COO bands typically observed in thespectra of peroxy radicals, we attribute some observed bands to low-frequency fundamentals corresponding to the OOCC bending of 2,1-HPP. This assignment is supported by both Franck-Condon simulations and experiments on jet-cooled radicals.
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? Organic peroxy radicals are important reactive chemical intermediates in tropospheric oxidation. ? The NIR electronic spectrum of 2,1-hydroxypropylperoxy radical is observed. ? The origin and vibrational bands of the three most stable conformers are observed and assigned.
Publication year: 2012 Source: Chemical Physics Letters, Available online 1 February 2012 Liwei Liu, Dongbo Li, Fenglan Bai One of the main tasks in biological sequence analysis is biological sequence comparison. Numerous efficient methods have been developed for sequence comparison. Traditional sequence comparison is based on sequence alignment. In this report, we propose a novel alignment-free method based on the relative Lempel-Ziv complexity to compare biological sequences. The vertebrate transferring genomes and the spike protein sequences are prepared and tested to evaluate the validity of the method. We use this method to build phylogenetic tree of two groups of the sequences. The result demonstrate that our method is powerful and efficient.
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? The main advantage is that this method can extract repeated patterns from biological sequence. ? The time complexity of this algorithm isO(l(Q) ×l(R)). ? We use this method to build phylogenetic tree. The result demonstrate that our method is powerful and efficient.
Publication year: 2012 Source: Chemical Physics Letters, Available online 2 February 2012 Yuya Yamagata, Yutaka Imamura, Hiromi Nakai This Letter explores the potential utility of the constrained self-consistent field (CSCF) method as an efficient methodology for estimating the external fields that reproduce desired physical quantities. Using the fact that a Lagrange multiplier introduced in CSCF corresponds to an external field (perturbation), numerical assessments of CSCF were carried out on the benzene molecule. The activation energies and critical electric fields that reverse the polarizations of the ferroelectric material tetrathiafulvalene-p-chloranil (TTF-CA) were efficiently estimated. The numerical assessments demonstrate the potential applicability of CSCF for the practical designs of materials possessing certain desired physical quantities induced by external fields.
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? We revisited constrained density functional theory in terms of material designs. ? We examined the physical meaning of a Lagrange multiplier in CSCF. ? Numerical stability of CSCF was examined for the benzene molecule. ? The activation energies and critical electric fields were efficiently estimated.
Publication year: 2012 Source: Chemical Physics Letters, Available online 2 February 2012 Kei Fujiwara, Atsushi Okazawa, Norimichi Kojima, Go Tanaka, Shunsuke Yoshii, ... Heterometallic pentanuclear coordination compounds [Ln4Cu] involving light lanthanide ions, Ce, Pr, Nd, Sm, and Eu, were synthesized and structurally characterized. The exchange interactions between the Ln and Cu ions were evaluated by high-frequency electron paramagnetic resonance and magnetization studies, clarifying the presence of ferromagnetic exchange couplings in Nd-Cu (JNd–Cu/kB= +0.30(6) K) and Sm-Cu (JSm–Cu/kB= +2.08(3) K), very small couplings in Ce–Cu and Pr–Cu, and the absence in Eu–Cu. A significant chemical trend is found in the order of the atomic number.
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? Exchange couplings were evaluated by high-frequency EPR and magnetization techniques. ? This method can be broadly applied to 3d-4f heterometallic complexes. ? The coupling is ferromagnetic for all of the light lanthanide Ln4Cu compounds. ? A chemical trend of the coupling parameter is found in the order of the periodic table.
Publication year: 2012 Source: Chemical Physics Letters, Available online 2 February 2012 Diego Carnevale, Geoffrey Bodenhausen Composite pulses of the typeallow one to excite the central transition of nuclei with half-integer spin with enhanced efficiency compared to a simplepulse. The method has been tested on solid samples containing sodium-23 (I= 3/2), aluminium-27 (I= 5/2) and scandium-45 (I= 7/2) under both static and magic-angle spinning conditions. Numerical simulations forI= 3/2 indicate that the enhancement is due to a more efficient conversion of Zeeman population differences associated with the satellite transitions to the central transition.
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? Excitation of the central transition of half-integer quadrupolar nuclei in solid state NMR. ? New composite pulse enhances the central transition by minimizing the creation of multiple-quantum coherences. ? The method is efficient under both static and spinning conditions.
Publication year: 2012 Source: Chemical Physics Letters, Available online 2 February 2012 A. Peralta Conde, V. Ovejas, R. Montero, F. Castaño The influence of water solvation on the photophysics of the indole chromophore has been investigated by revisiting the ultrafast relaxation of indole water clusters. The dynamics after excitation in the 284-234 nm energy range has been tracked by time delayed ionization with a 1305 nm probe. The results collected in the indole-mass channel, which were ascribed mainly to the indole-cluster fragmented by dissociative ionization, reflect a dynamical behavior analogous to that observed for the isolated indole molecule. The two femtosecond time constants observed in the transients were assigned to the coupling between theLaandLbsurfaces, and to the system evolution along the dissociativestate.
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? We studied the influence of the solvation on the dynamics of indole-water clusters. ? A time dependent study with femtosecond resolution of the dynamics is presented. ? The data permit the identification of the relaxation pathway to the ground state. ? A view of the water influence different from existing results is presented.
Publication year: 2012 Source: Chemical Physics Letters, Available online 3 February 2012 Sef Z. Riaz, Susanna L. Stephens, Wataru Mizukami, David P. Tew, Nicholas R. Walker, ... H2S?Ag?I was synthesised by a laser-ablation technique and characterised, both byab initiocalculations at the CCSD(T)(F12) level of theory and by rotational spectroscopy. The configuration at S is rigidly pyramidal, with no inversion on the microwave timescale. The experimental geometry [r0(S?Ag) = 2.4228(18) Å,r0(Ag?I) = 2.5416(9) Å,?0= 78.94(7)°] is in good agreement with that [re(S?Ag) =2.417 Å,re(Ag?I) =2.554 Å,?e= 77.0 °] calculatedab initio. The angular geometry of H2S?Ag?I is isomorphic with those of other members of the series H2S?Ag?X and with their hydrogen-bonded and halogen-bonded analogues H2S···HX and H2S···XY, respectively.
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? Synthesis of new compound H2S Ag?I. ? Rotational spectrum of H2S Ag?I. ? Ab inito calculations on H2S Ag?I. ? Geometry of H2S Ag?I.
Publication year: 2012 Source: Chemical Physics Letters, Available online 2 February 2012 Takunori Harada, Reiko Kuroda, Hiroshi Moriyama Because a circularly polarized luminescence (CPL) spectrophotometer is a polarization-modulation instrument, artifacts resulting from optical anisotropies that are unique to the solid state necessarily accompany CPL signals. A set of procedures for obtaining the true CPL signal has been derived based on the Stokes–Mueller matrix method. Experiments on chiral fluorophore single crystals of benzil with larger and smaller optical anisotropies have shown that our method can eliminate parasitic artifacts to obtain the true CPL signal, even in cases where optical anisotropies are substantial.
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? CPL signal was intrinsically influenced by the residual birefringence. ? An analytical method for obtaining artifact-free CPL spectra was newly developed. ? An analytical method is based on Stokes-Mueller matrix method. ? The procedure for true CPL measurements could eliminate artifact signals.
Publication year: 2012 Source: Chemical Physics Letters, Available online 31 January 2012 Jason N. Byrd, H. Harvey Michels, John A. Montgomery, Robin Côté An accurate long-rangeab initiopotential energy surface has been calculated for the ground statelithium trimer in the frozen diatom approximation using all electron RCCSD(T). Theab initioenergies are corrected for basis set superposition error and extrapolated to the complete basis limit. Molecular van der Waals dispersion coefficients and three-body dispersion damping terms for the atom-diatomic dissociation limit are presented from a linear least squares fit and shown to be an essentially exact representation of theab initiosurface at large range.
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? Ab initio surface of Li3 atom-diatom. ? Van der Waals expansion and separation of two body and many-body terms. ? Calculation of van der Waals terms by fitting.
Publication year: 2012 Source: Chemical Physics, Available online 30 January 2012 Takafumi Miyazaki, Ryohei Sumii, Hisashi Umemoto, Haruya Okimoto, Yasuhiro Ito, ... Ultraviolet photoelectron spectra (UPS) and X-ray photoelectron spectra (XPS) of two erbium atoms and an erbium-carbide cluster entrapped fullerenes, Er2@C82(I), Er2@C82(III), Er2C2@C82(I) and Er2C2@C82(III), were measured using a synchrotron radiation light source and MgK? X-ray gun. The spectral onset energy of these endohedral fullerenes is around 0.8-0.9 eV, which is larger than that of Er@C82(I) of 0.4 eV. The UPS of erbium atoms encapsulated endohedral fullerenes having the same C82cage structure were analogous while those of the different cage structure are different. This finding supports an empirical rule that the electronic structure of the endohedral fullerenes is principally governed by the C82cage structure. The XPS Er4d5/2peak of Er2@C82suggests the oxidation state of. The difference spectrum between the UPS of Er2@C82(III) and Er2C2@C82(III) has the sameC3vstructure reveals two excess electrons on the cage of Er2@C82.
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Highlight
? The UPS onset energy of endohedral fullerenes, Er2@C82(I), Er2@C82(III), Er2C2@C82(I) and Er2C2@C82(III), is around 0.8-0.9 eV.. ? The UPS of these endohedral fullerenes having the same C82cage structure were analogous while those of the different cage structure are different.. ? The XPS Er4d5/2peak of Er2@C82suggests the oxidation state of? The difference spectrum between the UPS of Er2@C82(III) and Er2C2@C82(III) has the sameC3vstructure reveals two excess electrons on the cage of Er2@C82...
Publication year: 2012 Source: Chemical Physics Letters, Available online 30 January 2012 Katsura Nishiyama, Kei Takata, Keiichi Watanabe, Hirotake Shigematsu We investigate solvation dynamics of organogel utilizing ps – ns fluorescence spectroscopy. The organogel studied in this work comprises bis(2-ethylhexyl) sulfosuccinate (AOT) andp-chlorophenol in them-xylene solvent, that produce an organogel architecture with self-assembly. Within the organogel, an emitting probe, coumarin 153 (C153), is embeded. We then obtain dynamic response functions of solvation derived from the time-resolved fluorescence spectra of C153. We propose that total energy of the C153 – organogel system relaxes with a relaxation time of 3.9 ns, whereas the entire rearrangement of the organogel structure around C153 is achieved with that of 6.1 ns, respectively.
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? Organogels are composed by self-assembly with hydrogen bonds and dispersion forces. ? An emitting probe, coumarin 153 is embedded inside the organogel structure. ? ps – ns fluorescence spectroscopy applied to measure dynamic fluctuations of gel. ? Spectral relaxations show dual aspects based on different modes of gel fluctuations..
Publication year: 2012 Source: Chemical Physics, Available online 26 January 2012 Zhijun Zhang, Bin Li, Zhitao Shen, Yinghui Renl, Wensheng Bian We present full-dimensional quantum mechanical calculations of the vibrational states of acetylene. The calculation scheme is a combination of several methods. The molecular Hamiltonian is represented in CH-CH diatom-diatom Jacobi coordinates. Phase space optimized discrete variable representation is used to construct effective one-dimensional basis functions for radial coordinates, and a basis contraction strategy is applied to angular coordinates. Parity and diatom-diatom permutation symmetry are exploited. The final Hamiltonian matrix is sparse, and an iterative technique combined with an efficient preconditioner is employed to calculate the eigenvalues within desired spectral windows. It is shown that our computation is efficient and accurate, and nearly ideal scaling with respect to increasing energy is achieved.
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? Full-dimensional calculations of vibrational states of acetylene are performed. ? The calculation scheme is accurate and efficient. ? Nearly ideal scaling with respect to increasing energy is achieved. ? The normal-to-local mode transition observed experimentally is confirmed.
Publication year: 2012 Source: Chemical Physics, Available online 27 January 2012 Simon Petretti, Alejandro Saenz, Alberto Castro, Piero Decleva Ionization and excitation of water molecules in intense laser pulses is studied theoretically by solving the three-dimensional time-dependent electronic Schrödinger equation within the single-active-electron approximation. The possibility to image orbital densities by measurement of the orientation-dependent ionization of H2O in few-cycle, 800 nm linear-polarized laser pulses is investigated. While the highest-occupied molecular orbitalis found to dominate the overall ionization behavior, contributions from the energetically lower lyingorbital dominate the ionization yield in the nodal plane of theorbital. The ratio of the ionization yields of the two orbitals depends on the intensity. Furthermore, even for laser pulses as long as 8 cycles the orientation-dependent ion yield depends on the carrier-envelope phase. In the interpretation of the orientation-dependent ionization as an imaging tool these effects have to be considered.
Graphical abstract
Three dimensional plots of the calculated normalized ionization (center column) and excitation (right column) yields of the HOMO of water. The shape of the individual orbitals (in real space) is given in the left column for comparison.
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? We study ionization and excitation of water in intense ultrashort laser pulses. ? The calculated yields reflect the shape of the molecular orbital densities. ? The ratio of the ionization yields of the HOMO and HOMO-1 depends on intensity.
Publication year: 2012 Source: Chemical Physics, Available online 27 January 2012 Grzegorz Mazur, Piotr Petelenz, Micha? Slawik Owing to the peculiar structure of oligothiophene crystals, their low-energyb-polarized spectra are dominated by the contributions from charge transfer states almost free from Frenkel state admixtures, offering a unique opportunity for in-depth studies of the former. Here, a simple model, rooted in the Mulliken theory of charge transfer transitions, is proposed to estimate the relevant transition dipole moments. For sexithiophene, the resultant estimate agrees with the value used in the recent detailed theoretical reproduction of the absorption and electroabsorption spectra, and is found to be consistent with other input parameters. The approach presented here is readily applicable for other one-component molecular crystals, providing a simple method to estimate the intrinsic transition dipoles of charge transfer configurations.
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? Intrinsic transition dipole moment of CT excitons in sexithiophene is evaluated. ? The underlying model is rooted in Mullikens theory of charge transfer transitions. ? The results agree with the values obtained by fitting the experimental spectra. ? The approach presented is applicable for other one-component molecular crystals.
Publication year: 2012 Source: Chemical Physics Letters, Available online 28 January 2012 Bin Xu, Congguo Long, Yusheng Wang, Lin Yi The electronic structure and transport properties were calculated for the filled-skutterudites LaFeB4BSbB12Bunder different pressures. The Fermi level shifts downward and the band gaps increase with the pressure increasing. The moving of Fe 3d and La 4d decides the physical properties of LaFe4Sb12with the different pressures. The Seebeck coefficient can be enhanced by increasing pressure and n-doping of LaFe4Sb12. Our calculation shows that the electronic conductivity?/?of LaFe4Sb12can be improved by doping. The peak value of the n-doped material increases faster than that of p-doped with increased pressure, indicating that the n-doping can greatly enhance the electrical transport properties of the LaFe4Sb12compound under high pressure.
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The power factorsS?/?of n-doped increase faster than that of p-doped with an increase of the carriers concentration in the low doping. The peak values of the n-doped increase faster than that of p-doped with an increase of pressure, indicating that the n-doped can greatly enhance the electrical transport properties of LaFe4Sb12compound under high pressure.
Highlights
? The Fermi level shifts downward and the band gaps increase with the pressure increasing. ? The moving of Fe 3d and La 4d decides the physical properties with the different pressures. ? The Seebeck coefficient can be enhanced by increasing pressure and n-doped of LaFe4Sb12. ? The electronic conductivity?/?can be improved by doping. ? The n-doped can greatly enhance the electrical transport properties under high pressure.
Publication year: 2012 Source: Chemical Physics Letters, Available online 26 January 2012 Yong-Jun Chen, Kosuke Suzuki, Hitoshi Mahara, Tomohiko Yamaguchi We report on a periodic precipitation pattern emerged from a drying meniscus via evaporation of a polystyrene solution in a Petri dish. It appeared a quasi-logarithmic spacing relation in the pattern as a result of stick-slip motion of the contact line towards the wall. A model based on the dynamics of the evaporating meniscus is proposed.
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? Gradient striped-patterns were prepared by dewetting at the meniscus region. ? Spacing in the pattern changed almost logarithmically but was slightly deviated. ? An equation was derived to describe the shape of the meniscus. ? A dynamic model is proposed for the stick-slip motion of the drying meniscus. ? The model explains the quasi-logarithmic spacing found in laboratory experiments.
Publication year: 2012 Source: Chemical Physics Letters, Available online 26 January 2012 Leon van Dijk, Frank C. Spano, Peter A. Bobbert We present a theory for the dynamics of excitons in molecular aggregates in presence of polaronic effects caused by a strong coupling to an intramolecular vibration. Transitions between exciton states are assumed to occur by weak coupling to low-energy acoustic phonons. The theory can describe measurements of the polarization anisotropy decay of helical aggregates of oligo(p-phenylene-vinylene) derivatives in solution. The fitted cut-off frequency of the acoustic phonons agrees well with an estimate of the Debye frequency of the solvent. The inclusion of polaronic effect leads for long times to a slower, but for short times to a faster exciton dynamics.
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? We develop a theory for exciton dynamics in molecular aggregates. ? Polaronic effects due to coupling to an intramolecular vibration are included. ? We model the polarization anisotropy decay in a helical molecular aggregate. ? Polaronic effects slow down dynamics at long times but speed it up at short times.
Publication year: 2012 Source: Chemical Physics Letters, Available online 26 January 2012 Shiji Krishnan, C.S. Suchand Sandeep, Reji Philip, Nandakumar Kalarikkal We report a novel functionality for the ferroelectric-antiferromagnet YCrO3powder of optical limiting upon illumination by nanosecond laser pulses at 532 nm. The optical limiting properties are investigated using the open aperturez-scan technique. The obtained nonlinearity fits to a three-photon like absorption mechanism. It is proposed that this nonlinearity is caused by two-photon absorption, followed by excited state absorption. Two different sized samples were investigated and the nonlinearity is found to be size dependent.
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? A novel functionality of YCrO3powders as optical limiter upon illumination by nanosecond laser pulses. ? The nonlinearity fits to a three-photon absorption mechanism. ? A two-photon induced excited state absorption is proposed. ? Size dependent optical limiting response.
Publication year: 2012 Source: Chemical Physics Letters, Available online 26 January 2012 G.-L. Chai, L.-J. Zhou, C.-S. Lin, Y. Yang, W.-D. Cheng The second-order nonlinear optical susceptibilities of ZnO single-walled nanotubes (SWNTs) were investigated by density functional theory. Both the zigzag and chiral ZnO SWNTs exhibit second-order nonlinear optical response while the armchair ZnO SWNTs have no response of second-order nonlinear optical behaviors. The d33is the largest component of second-order nonlinear optical susceptibility for both zigzag and chiral ZnO SWNTs, and it decreases as the diameter increase for zigzag ZnO SWNTs. The second-order nonlinear optical susceptibilities mainly originate from electronic transitions from O 2p states in valence bands to Zn 4p states in conduction bands.
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Highlights
? We have investigated NLO properties of ZnO SWNTs by using DFT calculations. ? Both zigzag and chiral ZnO SWNTs exhibit large second order NLO response. ? The NLO polarizabilities originate from transitions from O 2p in VB to Zn 4p in CB.
Publication year: 2012 Source: Chemical Physics Letters, Available online 28 January 2012 Ivan P. Pozdnyakov, Alexander V. Kolomeets, Victor F. Plyusnin, Alexey A. Melnikov, Victor O. Kompanets, ... Femtosecond pump-probe spectroscopy was used to determine the photophysical processes of Fe(III) complexes with citric and tartaric acids ([Fe(Cit)] and [Fe(tart)]) in aqueous solutions. The excitation of the complexes in the charge transfer bands is followed by formation of an intermediate absorbance decaying with two characteristic times. The shorter time constant (0.2, 1 ps) is ascribed to vibrational cooling and solvent relaxation of Frank-Condon excited state of corresponding complex and the second time constant (1.4, 40 ps) is assigned to superposition of internal conversion to the ground state and formation of the long-lived Fe(II) radical complex. The competition of these processes determines the quantum yield of photolysis of Fe(III)-carboxylates.
Graphical abstract
Highlights
? Fe(III) complexes with citric and tartric acids were investigated by ultrafast spectroscopy. ? Biexponential decay of transient absorbance was observed. ? Lifetimes and spectral properties of the excited states of the Fe(III) complexes were determined. ? Possible mechanism of the excited states decay were proposed and discussed.
Publication year: 2012 Source: Chemical Physics Letters, Available online 28 January 2012 Kazuhide Kamiya, Kazuhito Hashimoto, Shuji Nakanishi It is shown that thiocyanate ions (SCN) adsorbed on an electrode surface accelerate electrochemical reduction of Cu(II), resulting in the formation of CuSCN. The acceleration effect of adsorbed SCNions was proved by electrochemical impedance analysis and X-ray analyses of the resultant deposits. Importantly, spontaneous potential oscillation was observed during the Cu(II) reduction only in the presence of SCN, further evidenced the acceleration effect of the adsorbed SCN.
Graphical abstract
Highlights
? Adsorbed SCNions exhibit acceleration effect of Cu(II) electrochemical reduction. ? Potential oscillation was induced by the acceleration effect of adsorbed SCN. ? CuSCN and Cu are alternatively deposited in synchronization with the oscillation.
Publication year: 2012 Source: Chemical Physics, Available online 27 January 2012 Simon Petretti, Alejandro Saenz, Alberto Castro, Piero Decleva Ionization and excitation of water molecules in intense laser pulses is studied theoretically by solving the three-dimensional time-dependent electronic Schrödinger equation within the single-active-electron approximation. The possibility to image orbital densities by measurement of the orientation-dependent ionization of H2O in few-cycle, 800 nm linear-polarized laser pulses is investigated. While the highest-occupied molecular orbitalis found to dominate the overall ionization behavior, contributions from the energetically lower lyingorbital dominate the ionization yield in the nodal plane of theorbital. The ratio of the ionization yields of the two orbitals depends on the intensity. Furthermore, even for laser pulses as long as 8 cycles the orientation-dependent ion yield depends on the carrier-envelope phase. In the interpretation of the orientation-dependent ionization as an imaging tool these effects have to be considered.
Graphical abstract
Three dimensional plots of the calculated normalized ionization (center column) and excitation (right column) yields of the HOMO of water. The shape of the individual orbitals (in real space) is given in the left column for comparison.
Highlights
? We study ionization and excitation of water in intense ultrashort laser pulses. ? The calculated yields reflect the shape of the molecular orbital densities. ? The ratio of the ionization yields of the HOMO and HOMO-1 depends on intensity.
Publication year: 2012 Source: Chemical Physics, Available online 27 January 2012 Grzegorz Mazur, Piotr Petelenz, Micha? Slawik Owing to the peculiar structure of oligothiophene crystals, their low-energyb-polarized spectra are dominated by the contributions from charge transfer states almost free from Frenkel state admixtures, offering a unique opportunity for in-depth studies of the former. Here, a simple model, rooted in the Mulliken theory of charge transfer transitions, is proposed to estimate the relevant transition dipole moments. For sexithiophene, the resultant estimate agrees with the value used in the recent detailed theoretical reproduction of the absorption and electroabsorption spectra, and is found to be consistent with other input parameters. The approach presented here is readily applicable for other one-component molecular crystals, providing a simple method to estimate the intrinsic transition dipoles of charge transfer configurations.
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Highlights
? Intrinsic transition dipole moment of CT excitons in sexithiophene is evaluated. ? The underlying model is rooted in Mullikens theory of charge transfer transitions. ? The results agree with the values obtained by fitting the experimental spectra. ? The approach presented is applicable for other one-component molecular crystals.
Publication year: 2012 Source: Chemical Physics, Available online 25 January 2012 C. Sissa, F. Terenziani, A. Painelli, A.K. Manna, S.K. Pati Resonance energy transfer (RET) is investigated in a pair of polar charge-transfer (CT) chromophores, adopting essential-state models and time dependent density functional theory (TDDFT) calculations. Essential-state models describe in an efficient way linear and nonlinear optical properties of CT dyes, and prove very useful to rationalize the effects of electrostatic interchromophoric interactions on optical properties of multichromophoric systems. In this paper we adopt the same strategy developed for multichromophoric systems to investigate interchromophoric interactions responsible for RET. In the late forties, Th. Förster proposed a powerful method, based on the dipolar approximation, that directly relates the rate of the RET process to experimental accessible quantities. Here we discuss the applicability of the dipolar approximation for RET between CT dyes. The results obtained with essential-state models are confirmed by TDDFT calculations.
Graphical abstract
We discuss the range of applicability of the dipolar approximation to evaluate interchromophoric interactions responsible for resonance energy transfer (RET) between pairs of polar charge-transfer dyes.
Highlights
? The range of applicability of the dipolar approximation for the description of resonance energy transfer (RET) is examined for pairs of charge-transfer chromophores. ? Electrostatic interchromophoric interactions responsible for RET are naturally described by essential-state models. ? Essential-state models describe efficiently the energy-transfer phenomenon, and their results are in good agreement with more refined TDDFT calculations
Publication year: 2012 Source: Chemical Physics Letters, Available online 25 January 2012 Ridhima Chadha, Nandita Biswas, Ganesh B. Markad, Santosh K. Haram, Tulsi Mukherjee, ... We have succeeded in studying primary free radical reactions towards reduced graphene oxide (RGO) using pulse radiolysis technique. The ability of RGO to quench hydrated electron, eaq, can be visualized as a process to store electrons. Low reactivity ofOH and (SCN)2radicals towards RGO shows that oxidation process can be minimized at the surface of RGO. Moreover, it is found that methyl viologen radical also shows low reactivity towards RGO. Further, using RGO as a two-dimensional support, transient absorption spectra of Ag clusters show that stabilization of Ag2cluster occurs at the surface of RGO as compared to neat aqueous solution.
Graphical abstract
Reactivity of hydrated electron with RGO.
Highlights
? Hydrated electron reacts with reduced graphene oxide. ? Reactivity of hydroxyl and thiocyanate radicals is low towards reduced graphene oxide. ? Ionic clusters of silver interact with reduced graphene oxide.
Publication year: 2012 Source: Chemical Physics Letters, Available online 25 January 2012 Sung Il Ahn The effects of Ag surface plasmons (SPs) on the defects of ZnS are investigated. The photoluminescence (PL) spectra of ZnS on an Ag film show well resolved, enhanced, and red-shifted emissions compared to reference samples. The enhancement of the PL by the Ag layer is attributed to an enhanced energy transfer between overlapping band energies of ZnS by Ag SP. Based on the results, it is suggested that the PL emissions from defects can be enhanced and distinguished by SPs, which provide a direction for the application of SPs to characterize inorganic materials.
Graphical abstract
Highlights
? Effects Ag surface plasmons (SPs) on the defects of ZnS. ? Introducing defects to ZnS. ? Well resolved, enhanced, and red-shifted PL emissions from ZnS on Ag. ? Energy transfer between the absorption bands of the inter-band states and the surface states of ZnS by Ag SPs.
Publication year: 2012 Source: Chemical Physics Letters, Available online 27 January 2012 B. Bandyopadhyay, M.A. Duncan Doubly charged vanadium-water complexes are produced by laser vaporization in a pulsed supersonic expansion. Size-selected ions are studied with infrared photodissociation spectroscopy in the O-H stretch region using argon complex predissociation. Density functional theory calculations provide structures and vibrational spectra of these ions. The O-H stretches of V(H2O) appear at lower frequencies than those of the free water molecule or V(H2O). The symmetric stretch is more intensethan the asymmetric stretch in both V(H2O) and V(H2O) complexes. Spectra of V(H2O)Arn(n=2-7) show that the coordination of the Vis filled with six ligands, i.e. one water and five argon atoms.
Graphical abstract
The infrared photodissociation spectrum of V(H2O) tagged with four argon atoms. The vibrations are strongly red shifted from those of the isolated water molecule.
Highlights
? Vanadium cation complexes with water are produced in a molecular beam by laser vaporization. ? Ions are mass-selected and studied with IR photodissociation spectroscopy. ? O-H stretching frequencies are measured for V(H2O)Arncations for n=1-7 and m=1,2. ? Red-shifted O-H stretching frequencies are compared for complexes as a function of charge. ? The coordination of Vis filled with one water and five argon atoms.
Publication year: 2012 Source: Chemical Physics Letters, Available online 25 January 2012 Yufang Liu, Yonggang Yang, Kai Jiang, Deheng Shi, Jinfeng Sun The time-dependent density functional theory (TDDFT) method has been applied to investigate the excited states of 2?-deoxyguanosine (2?-dG) and its monohydrated complex (2?-dG-W1). The intramolecular hydrogen bonding N3•••H2-O2of the keto conformer is weakened in the S1state, while that of the enol conformers is strengthened. The two intermolecular hydrogen bondings of 2?-dG-W1 are weakened in the S1state, while N3•••H2-O2gets more strengthened. Moreover, the fluorescence of 2?-dG-W1 is shifted to higher frequencies compared with that of monomer 2?-deoxyguanosine. Therefore, it is concluded that the weakening of intermolecular hydrogen bonding in the S1state induces fluorescence strengthening of 2?-deoxyguanosine.
Graphical abstract
The fluorescence peaks of syn-enol and anti-enol conformers of 2?-deoxyguanosine are calculated to be 400 nm and 362 nm. After hydrogen bonded with water, the fluorescence peak of 2?-deoxyguanosine-W1blue-shifts to 328 nm, and the spectra intensity is also increased, which indicates the fluorescence strengthening of 2?-deoxyguanosine for the reason of intermolecular hydrogen bonding.
Highlights
? Intramolecular hydrogen bonds of keto and enol are different in excited states. ? Intermolecular and hydrogen bonds are both weakened in the S1state. ? Intermolecular hydrogen bond weakening induces fluorescence strengthening.
Publication year: 2012 Source: Chemical Physics Letters, Available online 25 January 2012 Guangrui Yao, Guanghan Fan, Haiying Xing, Shuwen Zheng, Jiahong Ma, ... Using the first-principles method based on the density functional theory, we study electronic and magnetic properties of GaN doped with 6.25% of V. The V dopants are found spin polarized and order ferromagnetically in GaN, with a magnetic moment of 2 ?Bper supercell. The V-doped GaN favors ferromagnetic ground state which can be explained in terms of double-exchange mechanism, and a Curie temperature above room temperature can be expected. Also, incorporation of V is easy. These results suggest that the V-doped GaN may present a promising dilute magnetic semiconductor and find applications in the field of spintronics.
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Highlights
? V-doped GaN favors ferromagnetic ground state. ? Ferromagnetism originates from double exchange mechanism. ? Ferromagnetic exchange interaction is short ranged. V-doped GaN is stable.
Publication year: 2012 Source: Chemical Physics Letters, Available online 25 January 2012 L. Messadia, G. El Dib, A. Ferhati, E. Roth, A. Chakir The UV absorption cross-sections of hydroxyacetone, 3-hydroxy 2-butanone, 4-hydroxy 2-butanone and 3-hydroxy 3-methyl 2-butanone have been measured. The experiments have been carried out between 250 K and 363 K using a D2 lamp coupled to a monochromator. This work provides the first UV cross-section measurements for 3-hydroxy 2-butanone, 4-hydroxy 2-butanone and 3-hydroxy 3-methyl 2-butanone. The obtained cross-section values are used to calculate the photolysis rates and to estimate the tropospheric lifetimes of the studied compounds. The results suggest that photolysis could be an important removal process for these species in the troposphere.
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Highlights
? The UV absorption cross-sections of a series hydroxycarbonyls have been measured. ? This work provides the first UV cross-section measurements for 4-hydroxy 2-butanone, 3- hydroxy 3-methyl 2-butanone and 3-hydroxy 2-butanone. ? Such data are required for laboratory studies concerning kinetic and photochemical measurements. ? The obtained cross-section values enabled us to estimate the tropospheric photolysis lifetimes of these compounds. ? The results suggest that photolysis could be an important removal process for these species in the troposphere.
Publication year: 2012 Source: Chemical Physics, Available online 20 January 2012 V.S. Yakovlev, M. Korbman, A. Scrinzi We propose a theoretical approach for the interpretation of pump-probe measurements where an attosecond pulse is absorbed in the presence of an intense laser pulse. This approach is based on abstractly defineddressed bound states, which capture the essential aspects of the interaction with the laser pulse and facilitate a perturbative description of transitions induced by the attosecond pulse. Necessary properties of dressed bound states are defined and various choices are discussed and compared to accurate numerical solutions of the time-dependent Schrödinger equation.
Graphical abstract
A comparison of the electron density obtained by numerically solving the time-dependent Schroedinger equation in the full Hilbert space with the electron density in the projected dynamical state.
Highlights
? An intense laser pulse affects the resonant absorption of an attosecond pulse. ? We axiomatically define bound states distorted by a strong ionizing electric field. ? Such dressed bound states are useful to interpret recent attosecond measurements. ? We compare and discuss several kinds of dressed bound states.
Publication year: 2012 Source: Chemical Physics, Available online 20 January 2012 Yang Li, Peng Wei, Meilin Bai, Ziyong Shen, Stefano Sanvito, ... The contact geometry and the electronic transport properties of Ag-benzene-Ag molecular junctions have been investigated by using first-principles quantum transport simulations. Our calculations show that a moderate benzene-silver interaction can be achieved when benzene is adsorbed on the Ag(111) surface through adatoms. In this case three symmetric Ag-benzene-Ag junction models can be constructed, in which the molecule is connected to the electrodes through one or two Ag adatoms on each side. Although the contribution to the transmission around the Fermi level made by benzene molecular orbitals depends on the number of Ag adatoms and the detailed binding configuration, the transmission coefficients at the Fermi level of the three junctions are calculated to be respectively 0.20, 0.18 and 0.16. These values are well consistent with the experimental one of 0.24±0.08. Our results thus demonstrate that the conductance of Ag-benzene-Ag junctions is rather stable regardless of the molecule/electrode contact geometry.
Graphical abstract
Fixed conductance value can be achieved for Ag-benzene-Ag junctions with different contact geometries.
Highlights
? We simulate Ag-benzene-Ag junctions with different contact geometries. ? Moderate benzene-Ag interactions can be realized for adsorptions through Ag adatoms. ? Molecular orbitals dominating the low-bias conductance match the contact symmetry. ? Three contact geometries deliver similar conductance consistent with experiments.
Publication year: 2012 Source: Chemical Physics, Available online 20 January 2012 Yasuo Nabekawa, Toshihiko Shimizu, Yusuke Furukawa, Eiji J. Takahashi, Katsumi Midorikawa We have demonstrated the interferometry of extreme ultraviolet (XUV) high-order harmonic fields of femtosecond Ti:sapphire laser pulses generated from the Xe gas target. We describe how we have measured the spatio-spectral fringes with an XUV spectrograph and extracted the interference traces from the measured spectrograms in detail. The comb-like structure in the spectrum ranging from the 11th to 17th order harmonic fields exhibits the periodical recurrence of interference fringes as an attosecond pulse train.
Graphical abstract
The interferometric trace of attosecond pulse train, formed with the 11th, 13th, 15th, and to 17th order harmonic fields is clearly observed with our autocorrelator setup. The fringes in both figures become clearly visible every 1.33 fs, corresponding to the half period of the pumping laser field, and the direction of each interference fringe is oopposite to that of the next fringe.
Highlights
? We have demonstrated the interferometry of extreme ultraviolet attosecond pulse train (APT). ? A spatial split autocorrelator is the crucial device for implementing the experiment. ? The Fourier spectrum of each harmonic field in the APT agrees well with the measured spectrum. ? The definite symmetry of the APT interference fringes is also revealed.
Publication year: 2012 Source: Chemical Physics, Available online 16 January 2012 Ramprasad Misra, Susmita Kar In this paper, we report the contrasting pattern of hydrogen bonding between solvents and 3-(phenylamino)-cyclohexen-1-one (PACO), an intramolecular charge transfer (ICT) molecule in the ground and excited states. The uniqueness of this molecule has been revealed through linear free energy based Kamlet - Taft analysis which indicates that the polarizability (??) and the hydrogen bond acceptor abilities (?) of the solvent are mainly responsible for the observed absorption spectra of the probe while polarizability (??) and the hydrogen bond donor abilities (?) of the solvents mainly determine its emitting profile. This investigation helps up to decipher the ground and excited state behavior of the hydrogen binding sites present in PACO. These findings are also expected to be useful in understanding the nature of other molecules containing multiple H-bonding sites.
Graphical abstract
The hydrogen bonding pattern of PACO with solvents in the ground and excited state has been investigated.
Highlights
? H-bonding pattern of PACO with solvents has been investigated experimentally. ? Both polarity and H-bonding ability of a solvent affect the photophysics of PACO. ? The nature of multiple H-bonding sites of this molecule has been deciphered.
Publication year: 2012 Source: Chemical Physics, Available online 9 January 2012 M. Franckevi?ius, R. Vaišnoras, M. Marcos, J.L. Serrano, A. Gruodis, ... Bonding of the promesogenic unit derived from 4-(4´-ethoxybenzoyloxy)salicylaldehyde to the amino terminated PPI dendrimer chains results in formation of the salicylidenimine chromophore groups. Absorption and fluorescence investigations of the dendrimer solutions supported by the quantum chemistry calculations revealed that the chromophore groups may exist in enol and keto tautomeric forms with relative concentrations depending on the dendrimer generation and solvent. The dendrimer fluorescence is attributed ton??states of keto tautomers which may also be formed from excited enol tautomers.
Graphical abstract
Tautomeric properties of PPI-SA dendrimers depend on their generation.
Highlights
? SA chromophore groups are formed by bonding terminal groups to PPI dendrimers. ? SA chromophore groups reveal four most stable tautomeric forms. ? Tautomeric properties of SA groups depend on the dendrimer generation and solvent. ? Aggregation of SA chromophores facilitates formation of thetrans-keto tautomers. ? Fluorescence of PPI SA dendrimers is attributed ton?states of keto tautomers..
Publication year: 2012 Source: Chemical Physics, Available online 8 January 2012 Qiong Ran, Chuan-Hui Zhang, Jiang Shen The structural stability and electronic properties of beryllium encapsulated in finite and infinite (3,0) zigzag BenSi6(n+1)nanowires were investigated using density functional theory. Results show that some finite (3,0) nanowires have higher binding energy than hexagonal prism ones, and they are energetically stable as increasing the number of Be. Mulliken population analysis shows that there are a few charges transfer from Si to Be atoms. The band gap of infinite nanowire is 0.024eV, exhibiting a characteristic of semiconductor. The deformation electron density shows the (3,0) nanowires aresphybridization, different from charge shielding of hexagonal prism nanowires. Therefore, BenSi6(n+1)nanowires may play important roles in spintronics and nanoelectronics in the future.
Graphical abstract
Some finite (3,0) nanowires have higher binding energy than hexagonal prism ones, and they are energetically stable as increasing the number of Be. Deformation electron densities of the (3,0) Be6Si42and hexagonal prism Be6Si42nanowires. (a) A blank ring is between Be and the outer Si ring indicating that an equilibrium state results from the charge transitions. (b) Three Be-centered orbitals that extend in three directions at angles of 120°, thereforesphybridization is apparent.
Highlights
? Silicenes, a monolayer of silicon atoms like grapheme may roll up silicon nanotubes. ? We study novel finite and infinite beryllium endohedral silicene-like silicon nanotubes. ? Their stability increases along with the tube length increasing. ? The band gap of infinite nanowire is 0.024eV, exhibiting a characteristic of semiconductor. ? The deformation electron density of (3,0) BenSi6(n+1)nanowires aresphybridization, different from charge shielding of hexagonal prism nanowires. Therefore, these properties will be very useful in spintronics.
Publication year: 2012 Source: Chemical Physics, Available online 9 January 2012 M. Franckevi?ius, R. Vaišnoras, M. Marcos, J.L. Serrano, A. Gruodis, ... Bonding of the promesogenic unit derived from 4-(4´-ethoxybenzoyloxy)salicylaldehyde to the amino terminated PPI dendrimer chains results in formation of the salicylidenimine chromophore groups. Absorption and fluorescence investigations of the dendrimer solutions supported by the quantum chemistry calculations revealed that the chromophore groups may exist in enol and keto tautomeric forms with relative concentrations depending on the dendrimer generation and solvent. The dendrimer fluorescence is attributed ton??states of keto tautomers which may also be formed from excited enol tautomers.
Graphical abstract
Tautomeric properties of PPI-SA dendrimers depend on their generation.
Highlights
? SA chromophore groups are formed by bonding terminal groups to PPI dendrimers. ? SA chromophore groups reveal four most stable tautomeric forms. ? Tautomeric properties of SA groups depend on the dendrimer generation and solvent. ? Aggregation of SA chromophores facilitates formation of thetrans-keto tautomers. ? Fluorescence of PPI SA dendrimers is attributed ton?states of keto tautomers..
Publication year: 2012 Source: Chemical Physics, Available online 8 January 2012 Qiong Ran, Chuan-Hui Zhang, Jiang Shen The structural stability and electronic properties of beryllium encapsulated in finite and infinite (3,0) zigzag BenSi6(n+1)nanowires were investigated using density functional theory. Results show that some finite (3,0) nanowires have higher binding energy than hexagonal prism ones, and they are energetically stable as increasing the number of Be. Mulliken population analysis shows that there are a few charges transfer from Si to Be atoms. The band gap of infinite nanowire is 0.024eV, exhibiting a characteristic of semiconductor. The deformation electron density shows the (3,0) nanowires aresphybridization, different from charge shielding of hexagonal prism nanowires. Therefore, BenSi6(n+1)nanowires may play important roles in spintronics and nanoelectronics in the future.
Graphical abstract
Some finite (3,0) nanowires have higher binding energy than hexagonal prism ones, and they are energetically stable as increasing the number of Be. Deformation electron densities of the (3,0) Be6Si42and hexagonal prism Be6Si42nanowires. (a) A blank ring is between Be and the outer Si ring indicating that an equilibrium state results from the charge transitions. (b) Three Be-centered orbitals that extend in three directions at angles of 120°, thereforesphybridization is apparent.
Highlights
? Silicenes, a monolayer of silicon atoms like grapheme may roll up silicon nanotubes. ? We study novel finite and infinite beryllium endohedral silicene-like silicon nanotubes. ? Their stability increases along with the tube length increasing. ? The band gap of infinite nanowire is 0.024eV, exhibiting a characteristic of semiconductor. ? The deformation electron density of (3,0) BenSi6(n+1)nanowires aresphybridization, different from charge shielding of hexagonal prism nanowires. Therefore, these properties will be very useful in spintronics.
Publication year: 2012 Source: Chemical Physics, Available online 3 January 2012 Michael Spanner, Serguei Patchkovskii Strong Field Ionization (SFI) and High Harmonic Generation (HHG) are the central processes that enable attosecond physics. To date, most theoretical investigations of SFI and HHG rely on semiclassical methods, most notably the strong field approximation (SFA), which treats the continuum states of the liberated electron as plane waves. SFA is a very successful conceptual model for atoms and small molecules, and leads to an intuitively satisfying picture of HHG (i.e. the three-step model). However, as SFI and HHG experiments enter the regime of polyatomic molecules, many approximations made in SFA-type models can no longer be ignored even for a qualitatively correct understanding. In this contribution, we present a selection of results from our efforts towardab initiomodelling of strong field processes in molecular systems. The method is applicable to single-electron ionization and HHG of gas-phase polyatomic molecular targets.
Graphical abstract
Please excuse me, but I don’t know what this is for….
Highlight
? Please excuse me, but I don’t know what this is for….
Publication year: 2011 Source: Chemical Physics, Available online 30 December 2011 Nicola Tasinato, Andrea Pietropolli Charmet, Paolo Stoppa, Santi Giorgianni, Alberto Gambi Halon 1113 (chlorotrifluoroethene), used in the synthesis of fluorocarbon-based polymers, has been recently detected in the atmosphere and it is a potential source of chlorine atoms. In this work, the vibrational properties of chlorotrifluoroethene are studied in the 125–5000 cmregion by coupling Fourier-transform infrared spectroscopy and high-levelab initiocalculations. The vibrational analysis is performed over the whole spectral range and band intensities are obtained in the range 400–3100 cm. Ab initiocalculations of the anharmonic force field are performed at the coupled cluster level of theory employing either cc-pVTZ or ANO basis sets. Vibration perturbation theory is applied to obtain spectroscopic parameters from the computed anharmonic force fields. The present results provide a solid interpretation of chlorotrifluoroethene vibrational spectrum, and they represent a significant reference for future studies on this molecule, being also the first published data on absorption cross sections andab initiocalculations.
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Highlights
? Halon 1113, potential ozone depleting gas, vibrational eigenstates and intensity. ? FT-IR experimental and theoretical study of chlorotrifluoroethene. ? Ab initio calculations at MP2 and CCSD(T) levels with cc-pVTZ and ANO basis sets. ? Equilibrium geometry and harmonic force field. ? Full CCSD(T) and hybrid anharmonic force fields..
Publication year: 2011 Source: Chemical Physics, Available online 28 December 2011 Anindita Shit, Sudip Chattopadhyay, Jyotipratim Ray Chaudhuri The transport property of a quantum Brownian particle that interacts strongly with a bath (in which a typical damping constant by far exceeds a characteristic frequency of the isolated system) under the influence of a tilted periodic potential has been studied by solving quantum Smoluchowski equation (QSE). By invoking physically motivated coordinate transformation into QSE, we have presented a transparent treatment for the determination of the effective diffusion coefficient of a quantum Brownian particle and the current (the average stationary velocity). Substantial enhancement in the efficiency of the diffusive transport is envisaged due to the quantum correction effects only if the bath temperature hovers around an appropriate range of intermediate values. Our findings also confirm the results obtained in the classical cases.
Graphical abstract
Variation of current with temperature.
Highlights:
? Transport of a quantum Brownian particle in a periodic potential has been addressed. ? Governing quantum Smoluchowsky equation (QSE) includes state dependent diffusion. ? A coordinate transformation is used to recast QSE with constant diffusion. ? Transport properties increases in comparison to the corresponding classical result. ? This enhancement is purely a quantum effect.
Publication year: 2011 Source: Chemical Physics, Available online 28 December 2011 John Gaff, Stefan Franzen Calculation of the dimensionless excited state displacements (ESD) using density functional theory (DFT) was used to estimate the resonance Raman cross sections of pyridine on Ag clusters using the time-correlator formalism. The model systems studied are supermolecules consisting of Ag clusters with bound pyridine, Agn-Pyr cluster (n = 2, 4, 8, 14 and 20). It was found that structural changes in pyridine observed in the ESD for all five Agn-Pyr supermolecular clusters were essentially equivalent, and similar to those observed for the strongly allowed 168 nm transition of free pyridine. Enhancements of ? 10– 10, were calculated for all Agn-Pyr clusters, which is comparable to the overall surface enhanced Raman spectroscopy (SERS) effect in studies of pyridine on Ag, suggesting that resonance Raman may be a significant contributor to the effect.
Graphical abstract
Highlights
? Ground and excited state geometry optimizations of pyridine on Ag. ? Calculates serve as starting point for time correlator methods. ? Raman cross sections calculated employing the two-time correlator method valid for all frequencies and temperatures. ? Results suggest that resonance Raman could be the dominate mechanism in SERS. ? Both charge transfer and metal d ? p band transitions can couple to raman active modes.
Publication year: 2011 Source: Chemical Physics, Available online 28 December 2011 Bo Shi, Fang Gao, WanZhen Liang A simplified approach for computing the electronic coupling of nonradiative excitation-energy transfer is proposed by following Scholes et.al.’s construction on the initial and final states (J. Chem. Phys. 102(1995)9574). The simplification is realized through defining a set of orthogonalized localized MOs, which include the polarization effect of the charge densities. The method allows calculating the coupling of both the singlet-to-singlet and triplet-to-triplet energy transfer. Numerical tests are performed for a few of dimers with different intermolecular orientations, and the results demonstrate that Coulomb term are the major contribution to the coupling of singlet-to-singlet energy transfer whereas in the case of triplet-to-triplet energy transfer, the dominant effect is arisen from the intermolecular charge-transfer states. The present application is on the Hartree-Fock level. However, the correlated wavefunctions which are normally expanded in terms of the determinant wavefunctions can be employed in the similar way.
Graphical abstract
Highlights
? We propose a simple method to calculate the coupling of singlet-to-singlet and triplet-to-triplet energy transfer. ? Coulomb term are the major contribution to the coupling of singlet-to-singlet energy transfer. ? Effect from the intermolecular charge-transfer states dorminates in triplet-to-triplet energy transfer. ? This method can be expanded by including correlated wavefunctions.
Publication year: 2011 Source: Chemical Physics, Available online 28 December 2011 Michael Miller, Frank J. Owens Density functional theory is used to calculate the bond dissociation energy to cleave the C60=C60bond of the paramagnetic X-C60=C60-X and X-C60=C60dimers where X is F, OH, O and H. The results show that these dimers would not be stable much above room temperature and therefore can not constitute the paramagnetic phase needed to form the observed ferromagnetism which has been shown to be stable up to 800 K. The calculated bond dissociation energies to remove an F, OH or H from a single C60are large suggesting that they could be the source of the unpaired spin needed for the high temperature ferromagnetism.
Graphical abstract
Highlights
? DFT is used to calculated the bond dissociation energy of functionalized C60dimers. ? The results show the dimmers would not be stable above room temperature. ? The calculations indicate the observed magnetism can not be due to C60 dimers. ? Because of their higher stability the ferromagnetism is likely due to X-C60monomers.
Publication year: 2011 Source: Chemical Physics, Available online 27 December 2011 A. Gumenyuk, N. Ostapenko, Yu. Ostapenko, O. Kerita, S. Suto The peculiarities of charge carrier traps’ energy spectra in poly (di-n-hexylsilane)films have been studied by the enhanced fractional thermally stimulated luminescence (TSL) in the temperature range of 5-200 ?. For the first time, we have shown that the majority of fractional energy values (>80%) is distributed between a set of horizontal energy levels suggesting a discontinuity of the traps’ energy spectrum. These data distinctly differ from the results of earlier studies where a quasilinear dependence of the activation energy on temperature was found. It is shown that the significant width of TSL bands originates from the dispersion of the frequency factor. It is also established that the values obtained for the activation energy correlate well with the frequencies of the symmetric Ramanactive Ag modes at 268 and 373 cm-1 of the silicon chain, which confirms the suggestion about the hole location on the segments of the silicon organic polymers backbone.
Graphical abstract
Temperature dependence of the activation energy of the traps for the as-prepared poly(di-n-hexylsilane) (PDHS) film.For the first time, a discrete structure of the traps’ activation energy is observed in TSL temperature dependence for the PDHS films. These data distinctly differ from the results of earlier studies where a quasi-continuous dependence of the activation energy on temperature was found. It is shown that the activation energies are distributed by three shelves at 0.034, 0.046 and 0.115 ?V. Obtained values of the activation energies of two traps practically coincide with the Agmodes of the Si chain observed in PDHS Raman spectrum atand. Thus, the total width of TSL curves is suggested to be due to the dispersion of the frequency factor rather than the traps’ energy dispersion.
Highlights
? The improved technique of the fractional TSL registration has been elaborated. ? The discrete energies of the charge carrier traps were observed for the PDHS film. ? The TSL activation energies correlate with the Raman Ag modes of the silicon chain. ? The width of TSL curve is generally due to the frequency factor dispersion.
Publication year: 2012 Source: Chemical Physics, Volume 392, Issue 1, 2 January 2012, Pages 215-220 [No author name available]
Posted on 24 December 2011 | 10:51 pm
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