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Chemical Physics - Verlag: Elsevier
'Chemical Physics' Und 'Chemical Physics Letters' veröffentlichen experimentelle und theoretische Arbeiten in den molekularen, biologischen Wissenschaften und den Materialwissenschaften.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): D.B. Jones , J.D. Builth-Williams , S.M. Bellm , L. Chiari , H. Chaluvadi , D.H. Madison , C.G. Ning , B. Lohmann , O. Ingólfsson , M.J. Brunger Triple differential cross section measurements for the electron-impact ionization of the highest occupied molecular orbital of tetrahydrofuran (THF) are reported. Experimental measurements were performed using the (e,2e) technique in asymmetric coplanar kinematics with an incident electron energy of 250eV and an ejected electron energy of 20eV. With the scattered electrons being detected at ?5°, the angular distribution of the ejected electrons was observed. These measurements are compared with calculations performed within the molecular 3-body distorted wave (M3DW) model, and against previous measurements on THF and tetrahydrofurfuryl alcohol to further understand the role that kinematics and structure play in electron-impact ionization.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Dai Taguchi , Takaaki Manaka , Mitsumasa Iwamoto , Kateryna Bazaka , Mohan V. Jacob By using electric-field-induced optical second-harmonic generation (EFISHG) measurement, we analyzed hysteresis behavior of capacitance–voltage (C–V) characteristics of IZO/polyterpenol (PT)/C60/pentacene/Au diodes, where PT layer is actively working as a hole-transport electron-blocking layer. The EFISHG measurement verified the presence of interface accumulated charges in the diodes, and showed that a space charge electric field from accumulated excess electrons (holes) that remain at the PT/C60 (C60/pentacene) interface is responsible for the hysteresis loop observed in the C–V characteristics.
Publication date: Available online 25 May 2013 Source:Chemical Physics Letters Author(s): Meng Ding , Dongxu Zhao , Bin Yao , Bin Zhao , Xijin Xu The ZnO microwires were synthesized repetitively via chemical vapor deposition method. The high power light emitting diode based on the single ZnO microwire/p-GaN heterojunction was realized. A strong ultraviolet emission accompanied by a relatively weak defects-related emission was observed at room temperature photoluminescence spectra of single ZnO microwire. The I-V curve of the heterojunction diode showed obvious rectifying characteristics with a turn-on voltage of about 7 V. Under the forward injection current of 1.1 mA, the ultraviolet electroluminescence centered at 389 nm wavelength could be obtained based on the single ZnO microwire/p-GaN heterojunction diode.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): O.S. Alekseeva , A.Z. Devdariani , M.G. Lednev , A.L. Zagrebin We report on the theoretical study of qusimolecular absorption and emission near the forbidden atomic line Cd induced by interaction with rare gas atoms (argon and krypton). With the use of the semiempirical method of quasimiolecular term analysis and the available experimental data, the potential curves for the Cd?+Kr and Cd?+Ar systems and the radiative widths were obtained. In the calculation the full semiempirical procedure was used for the first time. Also the probabilities of the transitions and the radiative lifetimes of the metastable states of Cd–Kr and Cd–Ar quasimolecules as functions of the vibrational excitation degree were calculated. Based on these semiempirical results the processes of the collision-induced quasimolecular absorption and emission near the forbidden atomic line in mixtures of Cd vapor with Ar and Kr atoms have been considered and the absorption coefficients, emission spectra and the total rate constants of radiative depopulation of the metastable state of Cd have been determined.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Xiaoqing Jia , Liang Chen , Junji Mizukado , Shuzo Kutsuna , Kazuaki Tokuhashi Using a relative rate method, rate constants of cyclo-CFCFCF2CF2–, cyclo-CHCFCF2CF2–, and cyclo-CHCHCF2CF2– reaction with OH radicals were determined to be (3.15±0.93)×10?13exp[(630±90)/T], (4.60±1.31)×10?13exp[(600±80)/T], and (3.28±0.57)×10?13exp[(190±50)/T] between 253 and 328K, and (3.79±0.11)×10?14, (6.15±0.16)×10?14, and (1.73±0.03)×10?13cm3molecule?1s?1 at 298K. The atmospheric lifetimes and GWPs for the 100year time horizon were estimated to be 1.02, 0.63, and 0.19years, and 119, 76, and 20.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Sotoodeh Bagheri , Hamid Reza Masoodi , Marziyeh Mohammadi , Mohammad Zakarianezhad , Batoul Makiabadi The influence of number of nitrogen atoms on some NMR data of aromatic azine?HF complexes has been investigated by B3LYP, PBE0 and PBE1KCIS methods using 6-311++G(d,p) basis set. Isotropic chemical shift of acidic hydrogen and the absolute value of 2hJN?F decrease by adding nitrogen atoms to ring. This behavior is reversed for 1hJN?H and 1JH–F coupling constants.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): P. Bornhauser , Y. Sych , G. Knopp , T. Gerber , P.P. Radi We re-visit the analysis of the vibronic sequence of the C2 Swan system published recently by Yeung et al. [1] in which the heavily perturbed (4,8) band could not be assigned and analyzed satisfactorily. Here, we outline the assignment of 122 transitions of the band by taking into account a recent deperturbation study of the , level by Bornhauser et al. [2]. Improved molecular constants for the , and , states are presented by performing a least-squares fit to the Hamiltonian with a favorable root-mean square error of 0.012cm?1.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): H. Pfeiffer , G. Klose , K. Heremans Calorimetric scans of a number of low-hydrated phospholipids provide quite complex heat capacity profiles during the thermotropic main phase transition. This short study proposes some explanations that are based on experimental data obtained from four different methods (DSC, 31P-NMR, 2H-NMR, X-ray diffraction).The preliminary results show for POPC in which way DSC data are related to the melting of the hydrocarbon chains. Furthermore, the quadrupolar splitting data obtained from the 2H-NMR spectra of hydration water reveal how the water reorientation might contribute to the main phase transition of phospholipids.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Enrique A. Castro , Alvaro Cañete , Paola R. Campodónico , Marjorie Cepeda , Paulina Pavez , Renato Contreras , José G. Santos The phenolysis of 3-nitrophenyl 4-cyanophenyl thionocarbonate (1) and 4-nitrophenyl 4-cyanophenyl thionocarbonate (2) are subjected to a kinetic investigation in order to evaluate the nucleofugality of the corresponding leaving groups. For the reaction of 2 only 4-nitrophenoxide is obtained as leaving group. For the reaction of 1 the nucleofugality ratio 3-nitrophenoxide/4-cyanophenoxide is 1/3 from the corresponding T? intermediate. Theoretical calculations confirm the experimental results. From these results it can be concluded that the non-leaving group affects the nucleofugality ratio.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Eiji Ohmae , Koichi Matsuo , Kunihiko Gekko To elucidate the contribution of tryptophan side chains to the vacuum-ultraviolet (VUV) circular dichroism (CD) of Escherichia coli dihydrofolate reductase, we measured the VUVCD spectra of eight tryptophan mutants down to 175nm. The difference spectra between the wild-type and the mutants clearly demonstrated that the contribution of tryptophan side chains extends to the high-energy peptide CD in the VUV region. These results should be useful for a theoretical study on improving protein secondary-structure analysis by VUVCD spectroscopy.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Katharine W. Moore Tibbetts , Richard Li , István Pelczer , Herschel Rabitz Predicting the chemical and physical properties of molecules often relies on systematic rules relating the properties to molecular characteristics. This Letter introduces a novel method to reveal predictive chemical rules based on analysis of the chemical property landscape, which specifies the functional relationship between a measured property and an appropriate set of molecular variables. As an illustration, we consider landscapes relating the 17O NMR chemical shift, 13C NMR chemical shift, and IR vibrational frequency to the moieties attached to a carbonyl group. Implications of this ‘Chemscape’ formulation for general molecular property prediction are discussed.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Tuan Hoang Vu , Mary Jane Shultz Knowledge of hydroxide ion’s spectral signature is an essential ingredient for finding it at the water surface. In solutions, the intense hydrogen-bonded resonance of water often hinders unambiguous characterization of the OH? stretching frequency and linewidth. These parameters are likely to be modified at the hydrophobic water–vapor interface. This communication reports the first experimental observation of hydroxide ion that is free from interaction with bulk water. OH? is isolated in a hydrophobic environment and exhibits a sharp resonance at 3634cm?1, as confirmed by isotopic substitution. The feature is red shifted from that of dangling OH bonds by 29cm?1.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Frank Gerlach , Daniela Täuber , Christian von Borczyskowski Optical confocal spectroscopy on self-assembled single nanoassemblies from CdSe/ZnS quantum dots (QD) and perylene diimide dye molecules demonstrates efficient Förster resonance energy transfer (FRET). Intramolecular dynamics of the flexible dye molecule change the FRET efficiency in course of the detection period of several minutes. This can be followed by correlated observations of luminescence intensities and related spectral shifts of both constituents. Contrary to several experiments on similar assemblies, the FRET efficiencies are by almost one order of magnitude larger in the non-polar liquid solvent TEHOS as compared e.g. to toluene. Experimental and theoretically expected efficiencies are in close agreement with each other.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Jianjun Liu , Shifu Chen , Qinzhuang Liu , Yongfa Zhu , Jinfeng Zhang The crystal structures, band structures, density of states and chemical bonding for NaBiO3 photocatalyst were performed using first principles method. The results indicated that NaBiO3 has an indirect band gap of about 2.20eV. The calculated positions of valence bands maximum and conduction bands minimum show that NaBiO3 has strong oxidation and reduction ability to decompose organic contaminants and split water to hydrogen under visible light irradiation. The distortion of BiO6 octahedra and the lighter effective mass of carriers facilitate the separation and migration of electronic and hole pairs and improve photocatalytic performance.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Kevin A. McDonnell , Nitin Wadnerkar , Niall J. English , Mahfujur Rahman , Denis Dowling An experimental and a hybrid density functional theory study of the photo-active and optical properties of bismuth ferrite (BFO) are presented. Phase-pure photo-catalytically active BFO was prepared experimentally with a 28% degradation of methyl orange observed over a 7-h period. Direct and indirect band gaps were measured to be 2.10 and 1.92eV, respectively. BFO was also studied computationally with the use of hybrid density functional theory, quite suitable for such a multiferroelectric material. This led to excellent, semi-quantitative agreement between hybrid DFT and experimental approaches for absorption coefficients.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Ke R. Yang , Xuefei Xu , Donald G. Truhlar We propose a new scheme for the direct diabatization of MC-QDPT wave functions. Our new scheme utilizes CASSCF diabatic molecular orbitals (DMOs); this is conceptually simpler than the previous approach and can lead to smoother diabatic potentials. We validated the new diabatization scheme, in comparison to CASSCF diabatization and to the original MC-QDPT diabatization scheme, for two test cases, the dissociation of LiF and the reaction of Li+FH?LiF+H. The results with our new scheme suggest that the new scheme with CASSCF DMOs would be a good choice for nonadiabatic dynamics studies in the future.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Franz Martinez , Najeh Rekik , Gabriel Hanna The equation-of-motion phase-matching approach provides an efficient way for calculating a system’s time-dependent polarization in any phase-matching direction subject to weak laser fields of arbitrary shape. Within this approach, we introduce the Poisson Bracket Mapping Equation and Forward–Backward methods, two approximate solutions of the quantum–classical Liouville equation, for simulating the laser-induced response of a quantum subsystem in a classical environment. We illustrate this approach by calculating the transient absorption signal in a model photo-induced condensed phase electron transfer reaction. The results are found to be in reasonable agreement with the exact results, which is promising for applications to realistic systems.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Hae Kyung Jeong , Xin Zhang , P.A. Dowben The electronic structure of poly(sodium 4-styrenesulfonate) intercalated graphite oxide (PSSGO) in the vicinity of the Fermi level was investigated using ultraviolet photoemission and inverse photoemission spectroscopies. The conduction band density of states for PSSGO is similar to that of graphite, indicating facile electron transfer from electrolyte ions to the PSSGO electrode in energy storage device applications. The in situ band gap of 1.9eV observed was smaller than that of graphite oxide by 0.4eV, helping to explain the high performance of electric double layer capacitor of PSSGO compared with graphite oxide.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Laxmikanta Dua , Prasanta K. Biswas Sol–gel based spin coated nanostructured films of tetragonal phase of antimony (10at%) doped tin oxide (ATO) were prepared on silica glass. XRD and TEM images identify the crystallite size lying in the range, ?3.4–9.8nm. Quantum confinement was observed in the nanoclusters. Evaluated band gaps at 3.62eV correspond to the transition for bulk ATO and 4.51eV, 5.26eV for excitons and oxygen deficiency. Schemes have been proposed for absorption and photoluminescence excitation (PLE). Two excitonic transitions were observed at 275nm and 310nm for different nanocluster sizes. Evaluation of mean free path and Fermi energy correspond to ionized scattering and degeneracy of the ATO films.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Hui Xie , Wen-Cai Lu , Wei Zhang , Peng-Hua Qin , C.Z. Wang , K.M. Ho Triangular graphene nanoflakes (GNFs) embedded in fluorinated graphene are systematically investigated using first-principles density functional theory (DFT) calculations. The electronic and magnetic properties of such nanoflakes depend sensitively on the topology (armchair or zigzag) and the length of the edge of nanofakes. All embedded armchair triangular GNFs are semiconducting with size-dependent band gaps. The embedded zigzag triangular GNFs are magnetic with a ferrimagnetic ground state due to topological frustration of the ? bonds. The magnetic moment scales linear with the size of the triangular GNF.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Yong Hui Lee , Jin Hyuck Heo , Sang Hyuk Im , Hi-jung Kim , Choong-Sun Lim , Tae Kyu Ahn , Sang Il Seok A vertically aligned TiO2 photoelectrode with sufficient space between TiO2 nanorods was synthesized by sacrificial templating of ZnO nanorods grown on a dense TiO2 layer/FTO film. The more expanded pore space in the TiO2 nanorod film than conventional mesoscopic TiO2 film greatly reduces the mass transport problem of cobalt electrolyte in the vicinity of the Sb2S3 sensitizer in Sb2S3-sensitized photoelectrochemical solar cells. Therefore, the nonlinearity of the power conversion efficiency (PCE) under illumination intensity was greatly relieved to 5.0% (0.1sun), 4.7% (0.5sun), and 3.7% (1sun) in a TiO2-nanorod-based Sb2S3-sensitized solar cell, whereas the efficiency of a mesoscopic-TiO2-based solar cell was significantly degraded to 5.3% (0.1 sun), 3.8% (0.5sun), and 2.3% (1sun).
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Konstantina Damianos , Riccardo Ferrando The structures of small Pd–Au clusters adsorbed on stepped MgO(100) are studied by Density-Functional Theory calculations, in the size range from 2 to 7 atoms for all compositions. A series of different structural motifs is singled out. These motifs are often in close energetic competition. It is shown that the adsorption in the vicinity of a step has strong effects on the preferential morphologies of these clusters. The driving forces for the stabilization of the lowest-energy structures are discussed.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Erik Busby , Arthur Thibert , Leah E. Page , Ali M. Jawaid , Preston T. Snee , Delmar S. Larsen The primary photodynamics of 5-nm CdZnS core, CdZnS/ZnS core/shell, and CdZnS/ZnS·Pd nanoparticle adducts are characterized with broadband ultrafast transient absorption spectroscopy. Photogenerated excitons in the CdZnS and CdZnS/ZnS nanoparticles exhibit long-lived (>20ns) lifetimes and further functionalizing of the type-I CdZnS/ZnS core/shells with Pd nanoparticles resulted in rapid exciton quenching (<250ps) due to the transfer of electrons from the CdZnS core into the Pd nanocrystals via tunneling through the insulating ZnS shell. The shell-induced surface trap passivation and near-unity charge carrier injection efficiency into a platinum-group metal nanoparticle shows potential for enhanced colloidal photocatalytic applications, while enhancing photostability.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Juan Rada , Roberto Cruz , Ivan Gutman A number of vertex-degree-based topological indices (TIs) can be expressed as a linear combination of the parameters , the number of edges with end vertices of degree i and j. We study the TIs of catacondensed hexagonal systems. Specifically, we introduce two operations, linearizing and unbranching, and show that TI is monotone with respect to these. As a consequence, we express TI in terms of the number of angular and branched hexagons. The catacondensed hexagonal systems for which TI assumes extremal values are characterized, as well as their TI-values derived.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Shigenori Tanaka , Miki Nakano Density functional theory for molecular fluids developed by Donley et al. (J. Chem. Phys. 101 (1994) 3205) is extended to include the effects of orientation-dependent bridge functions associated with the inter-particle, triplet correlations. Resultant integral equations for the pair and direct correlation functions are solved for water, where the three-body direct correlation functions are approximated in terms of two-body functions. A test calculation employing a simple Gaussian form for the two-body function between the oxygen sites then provides a promising result to improve the description of the oxygen–oxygen correlations in liquid water at room temperature.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Minyi Zhu , Lubos Mitas Accuracy of effective core potential (ECP) is studied for two sizes of cores by density functional theory, Hartree–Fock and quantum Monte Carlo (QMC) methods using the MnO molecule as a test system. We compare the energy differences between high-spin and low-spin states that were previously found to be problematic for transition metal oxide solids calculations with ECPs. In order to disentangle errors caused by ECPs and by subsequent methods used in calculations, we construct a scalar-relativistic He-core ECP for Mn atom. We find that within high quality correlated calculations both Ne-core and He-core ECPs provide energy differences with comparable, high accuracy.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Debasis Ghosh , Soumen Giri , Avinandan Mandal , Chapal Kumar Das In this letter hydrothermally synthesized hierarchical stacked nanoplate of Ni(OH)2 and Ag deposited Ni(OH)2 have been successfully fabricated on graphene nanosheet. The prepared Ni(OH)2, Ag deposited Ni(OH)2 and their graphene based composites were characterized by XRD, FESEM and TEM analysis. Graphene increases the utility of the pseudocapacitive Ni(OH)2 and Ag deposited Ni(OH)2 as electrode material. Electrochemical characterizations in 6M KOH electrolyte revealed superior electrode performance of the Ag deposited Ni(OH)2/graphene composite over Ni(OH)2/graphene composite with maximum specific capacitance of 496F/g at 1A/g current density accompanying 93% specific capacitance retention at the end of 500 consecutive charge discharge cycles.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Demeter Tzeli , Ioannis D. Petsalakis , Giannoula Theodorakopoulos A density functional theory study has been carried out on five carboxylic acid homodimers, free and encapsulated, in order to study the effect of encapsulation or compression. Attractive interactions between the guests and the walls of the capsules stabilize encapsulation even in cases of severe confinement where formation of dimers is unfavorable. Larger hydrogen bonds are calculated for the encapsulated than the isolated dimers except for the case of the bulkiest dimer considered, where encapsulation leads to shortening of the hydrogen bond. Shorter hydrogen-bond lengths with increasing size of the encapsulated dimers are calculated, in agreement with experimental work.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Hideaki Takahashi , Akihiro Morita This letter definitely evaluates inner pressures of microbubbles in liquid argon and water by molecular dynamics simulation. The microbubbles are modeled with spherical cavity, which circumvents most uncertainties about microscopic definition of curved surface and related quantities. In both liquids, the inner pressure deviates downward from the Young–Laplace equation when the cavity radius is smaller than two molecular diameters, and takes a maximum, about 900 and 3000atm, respectively, at the cavity radius being ?3Å. The hydrogen-bonding character of water plays little specific role in the deviation of the inner pressure.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Ali Hanoon Al-Subi , Alexander Efimov , Marja Niemi , Nikolai V. Tkachenko , Helge Lemmetyinen Evidence of the Marcus inverted region behavior for the forward electron transfer reaction in a double-linked zinc phthalocyanine–fullerene dyad was found. The charge separation and recombination processes of the dyad were studied in an ionic environment. The chloride ion coordination to the central zinc of the phthalocyanine macrocycle decreases the energy of the charge separated state and increases the energy of the phthalocyanine first singlet excited state, and thus increases the driving force for the charge separation and decreases it for the recombination. The charge separation is slowed down whereas the charge recombination is accelerated upon the chloride coordination.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Mariusz Szabelski , Piotr Bojarski , Zbigniew Wieczorek Ultraviolet absorption and fluorescence spectra were collected for para-substituted N,N-dimethylanilines in aqueous solution at various pH conditions. Two fluorescing forms were observed for all studied compounds, one protonated (ANsH+) and the second unprotonated (ANs) each of them with specific spectroscopic properties. Changing pH of solution results in the displacement of the equilibrium between two forms. It was found that protonated aniline derivatives in aqueous solutions undergo very fast excited-state proton dissociation and the pKa values obtained from absorption and fluorescence spectra are similar. The excited state values were calculated using the Förster cycle method.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Natasha A.D. Yamamoto , Lucas F. Lima , Rodolfo E. Perdomo , Rogério Valaski , Vanessa L. Calil , Andréia G. Macedo , Marco Cremona , Lucimara S. Roman The effect of poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid (PEDOT:PSS) modified with an amphiphilic fluoro compound was investigated on the performance of flexible organic solar cells in bilayer geometry and using substrate based on poly(ether-imide) (PEI) with ITO films with low resistivity and high optical transmittance. The poly[9,9?-dioctyl-fluorene-co-bithiophene] (F8T2) polymer and fullerene (C60) were used as electron donor and acceptor materials, respectively. The spin-casted PEDOT:PSS films had its sheet resistance reduced from 7M?sq?1 to 40k?sq?1 after a single step treatment with hexafluoroacetone (HFA), reflecting in an enhancement of power conversion efficiency in the photovoltaic cells from 0.45% up to 1.30%.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): C.Q. Jiao , S.F. Adams Cross sections of electron ionization of three isomeric xylenes, in an electron energy range of 10–200eV, are measured. The maximum total cross sections are observed at 80-eV electron energy to be 2.24, 2.10 and 2.05×10?15cm2 for m-xylene, p-xylene and o-xylene, respectively. The xylene compounds produce similar ion populations, with major product ions including C8H7,9,10+, C7H7+, C6H5–7+, C5H5+, C4H3+ and C3H3+. The similar ion populations can be explained through consideration of the fragmentation mechanism: essentially all fragment ions are formed via initial isomerization of the parent ions from the dimethylbenzene structures to the 7-methylcycloheptatriene structure.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Deming Han , Gang Zhang , Tian Li , Hongguang Li , Hongxing Cai , Xihe Zhang , Lihui Zhao The geometry structures, electronic structures, absorption, and phosphorescence properties of five heteroleptic cyclometalated osmium(II) complexes have been theoretically investigated. The lowest absorption of these complexes are located at 442, 441, 445, 439, and 446nm, respectively, and the HOMO?LUMO or HOMO?LUMO+1 is the predominant transitions. The lowest energy emissions of these complexes are localized at 620, 615, 616, 609 and 638nm, respectively. Ionization potential (IP) and electron affinity (EA) have been calculated to evaluate the injection abilities of holes and electrons into these complexes. The reorganization energies indicate complex 5 has the best electron injection ability and electron-transporting performance.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Kono H. Lemke , Terry M. Seward The M06-2X and B2PLYP-D functionals have been applied to predict structures and energies for (CO2)n clusters up to n=16. A comparison between M06-2X, B2PLYP-D and benchmark CCSD(T) results indicates that M06-2X is capable of providing accurate binding energies. Stepwise M06-2X (CO2)n clustering free energies exhibit a sharp discontinuity at the magic cluster size n=13 and systematically shift to more exergonic values with decreasing temperature, in particular for larger clusters. These results indicate that the M06-2X method provides an accurate and cost effective description of non-covalent interactions in (CO2)n clusters and therefore may provide important information on CO2 nucleation phenomena.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Wu Qin , Li Wei , Lei Wang , Changqing Dong , Xianbin Xiao , Zongming Zheng , Yongping Yang Following our previous work on the synergy between graphene and catalyst particle [1], we discuss how carbon nanotubes (CNTs) affect the catalytic reactivity of CuO during advanced oxidation processes using density functional theory calculations. CNTs act as electron donor and regulate the electronic structure of CuO during each reaction step because the 2p orbitals of the C atoms hybridise with the 4d orbitals of the Cu atoms rather than the 2p orbitals of the O atoms. An electric field guides charge transfer through the interface between the CNTs and CuO, which modifies the electronic state of CuO/CNTs for catalytic reactions.
Graphical abstract
Highlights
Electronic property of CuO/CNTs nanocatalysts.Catalytic effect of CuO/CNTs nanocatalysts for advanced oxidation processes.Conversion from ozone decomposition to hydroxyl radical generation over CuO/CNTs.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): J. M. R. Muir , H. Idriss The adsorption modes and electronic structure of formaldehyde on TiO2(110) were investigated using the PWDFT method. The ?1(O) adsorbed mode has two stable structures: perpendicular to surface plane and tilted along the [110] direction. The ?1(O) tilt geometry is ?25kJ/mol more stable than the ?1(O) straight geometry. In the case of tilted adsorption, orbital 2b2 of formaldehyde (HOMO; O2px) has considerable overlap with Ti3d states while in the case of perpendicular adsorption, orbital 5a1 (HOMO-2; O2pz) has the strongest overlap. All lower energy adsorbed formaldehyde orbitals have better Ti overlap in the straight configuration, however.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Martin Šulka , Michal Pito?ák , Ivan ?ernušák , Miroslav Urban , Pavel Neogrády We present the decomposition of interaction energies in beryllium clusters, , into a series of nonidentical m-body nonadditivities up to . We analyse the role of the electron correlation and compare nonadditivities at HF, CASSCF, MP2, CASPT2 and CCSD levels of theory with the reference aug-cc-pVTZ CCSD(T) results. The dominant nonadditivity terms are the three- and four-body. Five and six-body terms are relatively large in clusters, but the total interaction energy of is affected only marginally, due to their mutual cancellation.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Pablo A. Denis , Federico Iribarne The benzene–lithium complex is a prototype system to understand the interaction in lithium-doped nanocarbons. Herein, we have employed coupled-cluster theory and correlation consistent basis sets to study the C6v and C2v structures, of the C6H6·Li complex. We found that when the CCSD(T) method and large basis sets are employed, the C2V structure becomes lower in energy by 1.8kcal/mol. At the CCSD(T)/CBS level, and including corrections for core–valence and relativistic effects, the dissociation energy of the C2v (ionic) structure is 6.7kcal/mol whereas that corresponding to the C6v (nonionic) one is 4.9kcal/mol. Our results suggest that charge transfer in C6H6·Li does exist, in contrast with previous results.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): Dirk Zahn The atomistic mechanism of the perovskite?post-perovskite transformation of MgSiO3 is explored from molecular simulation mimicking extreme pressure and temperature conditions akin to planet Earth’s interior (D? region). The nucleation process is highly anisotropic and initiated by column-wise rotation of SiO6 octahedra around the [001] direction. The post-perovskite transition is found to be a rare event (i.e. one requiring substantial activation energy, ?15eV for the critical nucleus, but, once started, propagates very fast (103–104m/s). The most stable phase front, the (010) interface, propagates at only 10% of the speed of the (001) phase front.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Fei Dou , Carlos Silva , Xinping Zhang We find that the external quantum efficiency of photovoltaic diodes based on finely mixed blends of poly-9,9’-dioctylfluorene-co-bis-N,N’-(4-butylphenyl)-bis-N,N’-phenyl-l,4-phenylenediamine (PFB) and poly-9,9’- dioctylfluorene-co-benzothiadiazole (F8BT) depends strongly on the blend ratio. The peak external quantum efficiency is optimum for a PFB:F8BT ratio of 3:1. The difference of peak efficiency for this composition and a 1:1 ratio is significantly higher than the reported yield of charge-transfer excitons. From a surface topography analysis, we believe that charge percolation plays a crucial role in photocurrent efficiency in PFB:F8BT diodes. Furthermore, we present a qualitative model for different charge percolation pathways in diodes of different blend ratios.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Shailendra Kumar Verma , A.K. Mukherjee , I. Sinha Off-lattice Monte Carlo simulations in the NVT ensemble are employed to study the interaction forces between nanoparticles in Lennard-Jones (L-J) liquids. We consider solvophilic, neutral and solvophobic interactions between the solvent atoms and those that make up the nanoparticles. Neutral and solvophobic nanoparticles are found to coalesce even at intermediate distances. On the other hand, solvophilic nanoparticles are found to be more stable in solution due to the formation of a solvent shield.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Gian Giacomo Guerreschi , Markus Tiersch , Ulrich E. Steiner , Hans J. Briegel The yield of radical pair reactions is influenced by magnetic fields well beyond the levels expected from energy considerations. This dependence can be traced back to the microscopic dynamics of electron spins and constitutes the basis of chemical compasses. Here we propose a new experimental approach based on molecular photoswitches to achieve additional control on the chemical reaction and allow short-time resolution of the spin dynamics. Our proposal enables experiments to test some of the standard assumptions of the radical pair model and improves the sensitivity of a paradigmatic model of chemical magnetometer by up to two orders of magnitude.
Publication date: 6 June 2013 Source:Chemical Physics Letters, Volume 573 Author(s): R. Stephen Berry , Boris M. Smirnov A long-standing but rarely addressed challenge to physical sciences is reconciling or bridging between the macroscopic approach, exemplified by thermodynamics, continuum and infinite models, and the microscopic approach built from individual elements. Here, we show an approach to finding the boundary size region below which a microscopic approach is mandatory, and above which, one can use the macroscopic approach’s tools. We illustrate how to estimate this boundary size using examples from atomic clusters. The first reviews the boundary size above which the Gibbs Phase Rule is valid, but below, is inapplicable. Then we show how to find boundary sizes for other properties.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Ming Zhou , Jie Tang , Qian Cheng , Gaojie Xu , Ping Cui , Lu-Chang Qin Few-layer graphene has been prepared by electrochemical intercalation of graphite cathode using Na+/dimethyl sulfoxide complexes as intercalation agent. By adding thionin acetate salt into the electrolyte, the exfoliated graphite is stabilized and further exfoliated into few-layer graphene. Raman and X-ray photoelectron spectra indicate that the graphene material has lower content of defects and oxygen functional groups compared with that obtained by chemically reducing graphene oxide. The graphene paper produced by filtration shows an electrical conductivity of 380Sm?1, which is forty times larger than that of the graphene material produced by chemical reduction of thionin-stabilized graphene oxide.
Publication date: 30 May 2013 Source:Chemical Physics Letters, Volume 572 Author(s): Fazle Rob , Krzysztof Szalewicz A new algorithm is proposed for calculations of distributed molecular polarizabilities. In contrast to published algorithms, it virtually eliminates the charge-flow terms that result in a slower than inverse sixth power decay of dispersion energy whereas the remaining terms have unique and physically reasonable values. Dispersion energies computed from these polarizabilities are very close to unexpanded dispersion energies in the region of small charge overlap. The method is expected to provide reference data for development of dispersion functions used in simulations of biomolecules and in dispersion-supplemented density-functional approaches.
Publication date: 18 April 2013 Source:Chemical Physics, Volume 416 Author(s): Subhankar Sardar , Saikat Mukherjee , Amit Kumar Paul , Satrajit Adhikari We explore both the general symmetry-allowed accidental (SAA) conical intersections (CIs) and Renner–Teller (RT) interactions prevailed between the ground () and first excited () electronic states of in the configuration space of normal mode coordinates. Global ab initio potential-energy surfaces and Non Adiabatic Coupling Term (NACT) between those states are reported. For each of the three pairs of normal mode (), calculated NACT show singularity at different positions, which are used to calculate Adiabatic-to-Diabatic Transformation (ADT) angles and thereby, the diagonal elements of ADT matrix display (i) sign change for odd number of SAA CI (s) and (ii) no sign change for even number of SAA CIs as well as Renner–Teller interactions. Similar to Jahn–Teller CI, the existence of SAA CIs are, further, confirmed by Longuet-Higgins’ phase change.
Graphical abstract
Highlights
? Global ab initio potential surfaces (PES) of and states of NO2 are computed. ? Non Adiabatic Coupling Terms (NACTs) between those states are also calculated. ? Our Beyond BO theory confirms those PESs consist general SAA CIs and RT interaction. ? Singularities of NACT on normal mode coordinates indicate the presence of CI. ? Calculated Adiabatic to Diabatic Transformation matrix show sign change for CI.
Publication date: Available online 22 April 2013 Source:Chemical Physics Author(s): David Lennon , Robbie Warringham , Tatiana Guidi , Stewart F. Parker The hydrogenation of alkynes to alkenes over supported metal catalysts is an important industrial process and it has been shown that hydrocarbonaceous overlayers are important in controlling selectivity profiles of metal-catalysed hydrogenation reactions. As a model system, we have selected propyne hydrogenation over a commercial Pd(5%)/Al2O3 catalyst. Inelastic neutron scattering studies show that the C–H stretching mode ranges from 2850 to 3063cm?1, indicating the mostly aliphatic nature of the overlayer and this is supported by the quantification of the carbon and hydrogen on the surface. There is also a population of strongly hydrogen-bonded hydroxyls, their presence would indicate that the overlayer probably contains some oxygen functionality. There is little evidence for any olefinic or aromatic species. This is distinctly different from the hydrogen-poor overlayers that are deposited on Ni/Al2O3 catalysts during methane reforming.
Publication date: Available online 20 May 2013 Source:Chemical Physics Author(s): Anurag Sethi , Divina Anunciado , Jianhui Tian , Dung M. Vu , S. Gnanakaran As it remains practically impossible to generate ergodic ensembles for large intrinsically disordered proteins (IDP) with molecular dynamics (MD) simulations, it becomes critical to compare spectroscopic characteristics of the theoretically generated ensembles to corresponding measurements. We develop a Bayesian framework to infer the ensemble properties of an IDP using a combination of conformations generated by MD simulations and its measured infrared spectrum. We performed 100 different MD simulations totaling more than 10 microseconds to characterize the conformational ensemble of ?-synuclein, a prototypical IDP, in water. These conformations are clustered based on solvent accessibility and helical content. We compute the amide-I band for these clusters and predict the thermodynamic weights of each cluster given the measured amide-I band. Bayesian analysis produces a reproducible and non-redundant set of thermodynamic weights for each cluster, which can then be used to calculate the ensemble properties. In a rigorous validation, these weights reproduce measured chemical shifts.
Publication date: Available online 20 May 2013 Source:Chemical Physics Author(s): Rodrigo A. Cormanich , Lucas C. Ducati , Cláudio F. Tormena , Roberto Rittner Amino acid conformational analysis is widely studied in the literature. However, information about the intramolecular interactions that govern their conformational preferences is scarce and it is commonly attributed to intramolecular hydrogen bond formation. The present paper utilizes calculations at the B3LYP/aug-cc-pVDZ theoretical level and QTAIM and NBO methods for glycine, sarcosine and N,N-dimethylglycine conformers to emphasize that arbitrary literature interpretations are equivocal. Also, our results show that the interplay between steric and hyperconjugative interactions rules glycine conformer energies/geometries and such results are confirmed by sarcosine and N,N-dimethylglycine conformational preferences.
Publication date: Available online 25 April 2013 Source:Chemical Physics Author(s): Allen M. Ricks , Chantelle L. Anfuso , William Rodríguez-Córdoba , Tianquan Lian Time-resolved vibrational sum frequency generation (VSFG) spectroscopy has been used to investigate the vibrational relaxation dynamics of the rhenium bipyridyl CO2-reduction catalyst Re(CO)3Cl(dcbpy) [dcbpy=4,4?-dicarboxy-2,2?-bipyridine] adsorbed onto the (110) surface of a Rutile TiO2 single crystal. IR pump-VSFG probe spectra of the a?(1) CO stretching mode indicate a ultrafast population equilibration between three CO stretching modes followed by their population relaxation via intramolecular vibrational energy transfer. Similar vibational relaxation dynamics was also observed for the same complex on anatase TiO2 nanocrystalline thin films measured by IR pump-IR probe transient absorption spectroscopy. The relaxation dynamics of ReCOA on TiO2, in DMF solution, and immobilized on Au through alkane thiol linkers were compared to examine possible effects of adsorbate-TiO2 interaction.
Publication date: Available online 2 May 2013 Source:Chemical Physics Author(s): Nikolaos Tsapatsaris , Sven Landsgesell , Michael M. Koza , Bernhard Frick , Elena V. Boldyreva , Heloisa N. Bordallo Understanding polymorphism in pharmaceutical ingredients is a long-standing challenge in formulation science. A well-known example is paracetamol, C8H9NO2. The marketed stable form I crystallizes with corrugated molecular layers. In contrast, form II, which is thermodynamically favorable at high pressures, has relatively planar layers that can slip over each other without difficulty, but is metastable at ambient conditions. By means of inelastic neutron scattering we demonstrated that the lattice modes of form II exhibit a sudden 1meV energy shift at 300K under a pressure of ca 0.4GPa. Moreover, evidence of an increase of the vibrational energy in both polymorphs was found, which was accompanied, in form I, by an unexpectedly weak increase of the tunnel splitting. These results indicate an anisotropy of the potential surface probed by the methyl rotor, and are discussed in relation to the differences of the strength of the hydrogen bond environment for each polymorph.
Publication date: Available online 30 April 2013 Source:Chemical Physics Author(s): Michael J. Wilhelm , William McNavage , Jonathan M. Smith , Hai-Lung Dai We have used time-resolved IR emission spectroscopy to examine collision induced intersystem crossing (CIISC) and deactivation of vibronically excited cis-HCCO(), generated following the 193 nm photolysis of ethyl ethynyl ether, by inert gases: He, Ar, and Xe. Observation of vibrationally excited CO(), in experiments quenched with Ar or Xe, suggest rapid CIISC due to a heavy-atom effect. Conversely, experiments quenched with He show transient signal from cis-HCCO(), and a distinct absence of CO(), suggesting that CIISC occurs only after cis-HCCO() has been quenched (i.e., CIISC is significantly less efficient with He). Inert gas CIISC rate constants for cis-HCCO() were deduced to be =(4.30.2)=(8.10.2), and =(13.00.1). Additionally, we report the first experimental assignment of 178536 cm?1 for the fundamental transition of the asym-CCO stretch of cis-HCCO(), which, compared with ab initio calculations, suggests that cis-HCCO() exhibits positive anharmonicity.
Publication date: Available online 22 May 2013 Source:Chemical Physics Author(s): Dan Bing , Toru Hamashima , Chen-Wei Tsai , Asuka Fujii , Jer-Lai Kuo The dependence of the preferential protonated site in (CH3)3N-H+-(CH3OH)n on the cluster size was investigated using theoretical calculations and infrared spectroscopy measurements. While simple estimation from the magnitude of proton affinity suggested that the excess proton prefers the methanol site in n ? 4, density functional theory calculations of the stabilization energy indicated the clear preference as protonation of the trimethylamine site, even for n = 9. Infrared spectra of the clusters were observed for n = 3-7. Spectral simulations were also performed using the quantum harmonic superposition approximation. The observed (CH3)3N-H+-(CH3OH)n spectra were well interpreted by simulations of the isomers with the protonated trimethylamine ion core. It was shown that both the proton affinity and the mutual solvation energy govern the preferential location of the excess proton in binary component clusters.
Publication date: Available online 23 May 2013 Source:Chemical Physics Author(s): B. Zgardzi?ska , T. Goworek The ortho-positronium (o-Ps) lifetime and intensity in cyclohexane was measured as a function of temperature at various wavelengths of illuminating light. Accommodation of excess electrons in traps was observed in whole range of rigid crystalline phase; the trap depth was about 0.75 eV.At the wavelength ? < 880 nm a slight decrease of o-Ps lifetime in rigid phase was observed, which could be explained by photoionization of Ps atoms. The binding energy of hydrogenlike Ps atom confined in a void is smaller than that of free atom. The lifetime of o-Ps in plastic phase corresponds to that expected for positronium located in vacancies. The radii of voids obtained from the popular Tao-Eldrup model seem to be too small for the lifetimes of order of 1 ns.Oxygen from surrounding atmosphere begins to penetrate the cyclohexane in plastic phase already 15 K below the melting point.
Publication date: Available online 23 May 2013 Source:Chemical Physics Author(s): Martin Owen Jones , David M. Royse , Peter P. Edwards , William I.F. David The synthesis of the magnesium halide ammines (Mg(NH3)6Cl2, Mg(NH3)6Br2 and Mg(NH3)6I2) is reported and their structures are identified by high resolution X-ray diffraction. The structures of Mg(NH3)6Br2 and Mg(NH3)6I2 are reported for the first time. The desorption properties of Mg(NH3)6Cl2, Mg(NH3)6Br2 and Mg(NH3)6I2 are examined by thermogravimetric analysis and NMR, and the trends in desorption properties as a function of composition are interpreted using a simple ionic model. It is found that the desorption properties are dependent on the lattice enthalpy of the intermediate and final phases Mg(NH3)2X2, Mg(NH3)X2 and MgX2, that the anion has limited effect on the state of Mg-N bonding and that the desorption temperature of ionic ammines may be tuned by varying the size of the anion.
Publication date: Available online 16 May 2013 Source:Chemical Physics Author(s): S. Magazù , F. Migliardo , B.G. Vertessy , M.T. Caccamo In the present paper the results of a wavevector and thermal analysis of Elastic Incoherent Neutron Scattering (EINS) data collected on water mixtures of three homologous disaccharides through a wavelet approach are reported. The wavelet analysis allows to compare both the spatial properties of the three systems in the wavevector range of Q=0.27 Å-1 4.27 Å-1. It emerges that, differently from previous analyses, for trehalose the scalograms are constantly lower and sharper in respect to maltose and sucrose, giving rise to a global spectral density along the wavevector range markedly less extended. As far as the thermal analysis is concerned, the global scattered intensity profiles suggest a higher thermal restrain of trehalose in respect to the other two homologous disaccharides.
Publication date: Available online 11 May 2013 Source:Chemical Physics Author(s): Stewart F. Parker Ab initio calculations of the complete unit cell of L-cysteine for both the orthorhombic and monoclinic polymorphs have been carried out. The results suggest the presence of a previously unrecognised, weak dihydrogen bond of a novel type: S–H···N–H in the gauche conformer of the monoclinic polymorph. Comparison of the calculated transition energies to those observed in the infrared, Raman and inelastic neutron scattering spectra of the orthorhombic form shows excellent agreement, as does the simulated INS spectra to that experimentally measured. The assignments are in general agreement with those in the literature but differ in detail. The strong intermolecular interactions present make the use of periodic-DFT essential in order to correctly assign the spectra. The need for, and the complementarity of, all three types of vibrational spectra: infrared, Raman and INS is clearly demonstrated.
Publication date: Available online 23 May 2013 Source:Chemical Physics Author(s): T. Mahadevan , M. Kojic , M. Ferrari , A. Ziemys We report results from molecular simulations that reveal the causes of reduced diffusivity at solid-liquid interfaces in the presence of nanoscale confinement. The diffusion of a 2M glucose solution was simulated inside a 10nm silica channel together with the calculated thermodynamic properties of diffusion. A strong energy-entropy compensation mechanism was found at the interface with a free energy minimum of -0.6kcal/mol. Using the Eyring equation the average jump length was reduced by 15% at interface. The complete loss of solute diffusivity at silica surface was explained by the substantial loss of the probability of productive displacements. The results suggested that glucose molecule diffusivity close to the surface might be related to a stiffer cage of the hydration shell, which affects the probability of cage breaking. These results help in understanding of diffusion mechanisms at interface and predicting mass transport in nanoconfinement for engineering and biomedical applications.
Publication date: 3 June 2013 Source:Chemical Physics, Volume 418 Author(s): Rajesh Kumar , Rishu Jain , Rajesh Kumar To determine the effect of solvent viscosity on low-frequency local motions that control the slow changes in structural dynamics of proteins, we have studied the effects of solvent viscosity on the structural fluctuation of presumably the M80-containing ?-loop by measuring the rate of thermally-driven CO-dissociation from a natively-folded carbonmonoxycytochrome c (NCO-state) in the 0.65–92.5cP range of viscosity at pH 7.0. At low viscosities (?8cP), the rate coefficient, kdiss for dissociation of CO from the NCO-state varies inversely with the viscosity, but saturates at high viscosities, suggesting that CO-dissociation reaction involves sequential stages that depend differently on solvent friction, i.e., solvent coupled and nonsolvent-coupled stages of the process. In the low viscosity regime (0.65??s?8.0cP), the rate-viscosity data were fitted to modified Kramers model, kdiss=[A?/(?+?s)n]exp(??G/RT), which produced internal friction, ?=1.35cP (±0.88), which suggests that the speed of CO-dissociation from NCO at ?s?8.0cP is controlled by internal friction.
Publication date: 3 June 2013 Source:Chemical Physics, Volume 418 Author(s): K. Brose , A. Zouni , F. Müh , M.A. Mroginski , J. Maultzsch In order to clarify possibilities to identify the -carotene (-Car) radicals in secondary electron transfer (ET) reactions in the photosystem II core complex (PSIIcc), Raman intensities of all 96 -Car cofactors in the unit cell of PSIIcc-dimer crystals as a function of polarisation and crystal orientation were simulated based on the 2.9Å resolution structure. The Raman-active symmetry Ag in the group is assigned to the -Car modes and . Simulations are in agreement with experiment for off-resonant excitation at 1064nm. Resonant measurements at 476 and 532nm excitation can not be explained, which is attributed to mode mixing in the excited state and the existence of different spectral pools. The identity of the -Car oxidised in secondary ET can not be resolved by Raman measurements on PSIIcc-dimer crystals. Additional simulations show that similar measurements on PSIIcc-monomer crystals could provide a possible route to solve this issue.
Publication date: 16 May 2013 Source:Chemical Physics, Volume 417 Author(s): Vikas Chauhan , Prasenjit Sen Structural, electronic and magnetic properties of 3d transition metal doped strontium clusters are studied using first-principles electronic structure methods based on density functional theory. Clusters with enhanced kinetic and thermodynamic stability are identified by studying their hardness, second order energy difference and adiabatic spin excitation energy. CrSr9 and MnSr10 are found to have enhanced stability. They retain their structural identities in assemblies, and are classified as magnetic superatoms. A qualitative understanding of the magnetic coupling between two cluster units is arrived at. Reactivity of these superatoms with O2 molecule is also studied. Prospects for using these magnetic superatoms in applications are discussed.
Publication date: 16 May 2013 Source:Chemical Physics, Volume 417 Author(s): Emily A.A. Jarvis , Brian Lee , Bradley Neddenriep , Wendy Shoemaker A computational comparison of key steps along proposed water oxidation pathways for eleven distinct mononuclear ruthenium catalysts is presented. Free energies are determined via density functional calculations and analyzed for catalyst structural stability, energetic comparisons to experimentally measured potentials in highly acidic conditions, and other features. A single feature for optimal catalyst design does not emerge; different steps along the oxidation cycle are impacted in subtle and sometimes divergent ways depending on the nature of the ligand modification on the catalyst. The results reinforce the notion observed in previous experimental studies – in such multi-step mechanisms with complex catalysts, a careful balance between energetic optimization and catalyst stability at multiple steps along the cycle may be critical for practical performance considerations. Whereas comparing catalysts at an individual step is likely to provide an incomplete picture, behavior of chemically modified catalysts can be distinguished computationally across multiple mechanistic steps.
Publication date: 16 May 2013 Source:Chemical Physics, Volume 417 Author(s): Yang Liu , Isaac B. Bersuker , James E. Boggs The Pseudo Jahn–Teller Effect (PJTE) is employed to explain the origin of the puckered structure of cyclobutadiene dication () and rationalize its difference from the less-folded and planar analogs. It is found that in the highest-symmetry D4h configuration of all three dications, the vibronic coupling between the ground state 1A1g and excited state 1B2u, i.e., the PJTE problem (1A1g+1B2u)?b2u, is the reason of puckering instability. In the PJTE interaction is very strong breaking the D4h symmetry to form a stable D2d puckered geometry, whereas in it is relatively weak resulting in a less-folded structure. Compared with and , the PJTE interaction in is very weak due to the extremely large energy gap of 9.64eV between the two coupling states, so no puckering instability occurs.
Publication date: 3 June 2013 Source:Chemical Physics, Volume 418 Author(s): Pardis Simon , Katia March , Odile Stéphan , Yann Leconte , Cécile Reynaud , Nathalie Herlin-Boime , Anne-Marie Flank This work presents a structural study by X-ray Absorption Spectroscopy (XAS) and Electron Energy-Loss Spectroscopy (EELS) of complex titanium oxynitride nanoparticles (Ti(O,N)), synthesized by laser pyrolysis from titanium tetraisopropoxide and ammonia as precursors. Previous structural characterizations obtained by XRD and XPS have shown that the nanoparticles present a TiO type face-centered cubic (FCC) structure but with three different oxidation degree for titanium. The synthesis of this kind of titanium oxide or oxynitride nanoparticles is very unusual. Moreover, their properties are highly dependent of their structure. EELS spectrum-imaging data were therefore used for mapping the different chemical species. These measurements reveal that the nanoparticles are composed of a FCC solid solution of nitrogen and oxygen in titanium. The local structure around Ti was then studied. XANES measurements show an absorption threshold corresponding to a global valence state between Ti3+ and Ti4+, with a pre-edge structure characteristic of a mix between a face-centered cubic (FCC) structure and a disordered TiO2 structure whereas the EXAFS signal is dominated by the contribution of the FCC structure. Oxidative heat-treatments have been performed from 250 to 450°C in order to follow the transition towards the dioxide phase. EELS measurements show that the oxidation occurs from the surface of the nanoparticles. XAS show that this transition does not involve any other crystallographic phase than TiO2, mainly in its anatase form, and seems to occur via a dioxide disordered phase. The FCC contribution completely disappears at 450°C where the sample reaches a complete TiO2 structure. Moreover, a correlation is established between the structural evolution and optical properties.
Publication date: 3 June 2013 Source:Chemical Physics, Volume 418 Author(s): Seifollah Jalili , Maryam Jamali , Jeremy Schofield The lithium adsorption energies and electronic structures of pristine ((8,0)) single-walled carbon nanotube (SWCNT) and functionalized carbon nanotubes with amine and carboxyl groups (NH2/((8,0)) and COOH/((8,0))) were studied using density functional theory. The results show that the adsorption energies of lithium inside and outside of ((8,0)) SWCNT differ very little from each other. When the lithium is doped in carbon nanotubes, charge transfer takes place from the lithium to the nanotubes. After functionalization of carbon nanotubes with amine (NH2) and carboxyl (COOH) groups, various positions for lithium adsorption around the functional groups can be served. The adsorption energy of lithium in these positions is greater than that of lithium in pure ((8,0)) SWCNT. When the lithium was doped in NH2/((8,0)) and COOH/((8,0)), an energy gap between valence and conduction bands is observed, and the conductivity is reduced relative to lithium-doped non-functionalized carbon nanotubes.
Publication date: 3 June 2013 Source:Chemical Physics, Volume 418 Author(s): Koich Furuta , Masanori Fuyuki , Akihide Wada To understand the elementary steps of chemical reactions, unimolecular reactions are important and considered to be model reactions. We carried out pump–probe and two-pulse correlation (2PC) measurements of the multiphoton-induced reaction of DTTCI (3,3?-diethyl-2,2?-thiatricarbocyanine iodide), a kind of cyanine dyes, under the red-tail excitation condition and found that both photoisomerization and photodegradation were caused by a two-photon process and the reaction time for photoisomerization was approximately 0.5ns. Excitation dynamics was examined by 2PC measurements and the temporal character of the intermediate state was analyzed.
Publication date: 18 April 2013 Source:Chemical Physics, Volume 416 Author(s): Haining Liu , Jason E. Bara , C. Heath Turner A deeper understanding of the acid/base properties of imidazole derivatives will aid the development of solvents, polymer membranes and other materials that can be used for CO2 capture and acid gas removal. In this study, we employ density functional theory calculations to investigate the effect of various electron-donating and electron-withdrawing groups on the proton affinity of 1-methylimidazole. We find that electron-donating groups are able to increase the proton affinity relative to 1-methylimidazole, i.e., making the molecule more basic. In contrast, electron-withdrawing groups cause a decrease of the proton affinity. When multiple substituents are present, their effects on the proton affinity were found to be additive. This finding offers a quick approach for predicting and targeting the proton affinities of this series of molecules, and we show the strong correlation between the calculated proton affinities and experimental pKa values.
Publication date: Available online 29 April 2013 Source:Chemical Physics Author(s): Charoensak Lao-ngam , Mayuree Phonyiem , Sermsiri Chaiwongwattana , Yoshiyuki Kawazoe , Kritsana Sagarik Characteristic NMR spectra of proton transfer in protonated water clusters were studied using the H+(H2O)n complexes, n = 2–5, as model systems, and ab initio calculations at the RIMP2/TZVP level and BOMD simulations as model calculations. Based on the concept of presolvation, two-dimensional potential energy surface of proton in the smallest, most active intermediate complex (the Zundel complex) was constructed as a function of the H-bond distance (RO-O) and the asymmetric stretching coordinate (?dDA). The low-interaction energy path and the path with ?dDA = 0 Å were analyzed and discussed in comparison with the model systems. The two proton transfer paths associate with the characteristic IR frequencies namely, the structural diffusion and oscillatory shuttling frequencies, respectively. RIMP2/TZVP calculations showed that the proton moving on the oscillatory shuttling path is characterized by the 1H NMR shielding constant (?H+corr) varying in a narrow range, whereas on the structural diffusion path, ?H+corr changes exponentially with RO-H. The energetic, dynamic and spectroscopic results obtained from BOMD simulations in the temperature range between 350 and 450 K validated the presolvation model and revealed that the activation energies for the proton exchange in the smallest, most active intermediate complex, computed from the Arrhenius equation, IR spectra and a simple 1H NMR line shape analysis, are consistent and in good agreement with experiments in aqueous solution. Based on the presolvation model and the outstanding characteristics of the IR and 1H NMR spectra of the transferring protons, the present theoretical study suggested framework and steps to investigate structural diffusion processes in strong, protonated H-bond systems.
Graphical abstract
Highlights
Characteristic 1H NMR shielding constants of the proton on the oscillatory shuttling (A) and structural diffusion paths (B).
Publication date: 3 June 2013 Source:Chemical Physics, Volume 418 Author(s): Masahide Ohno The L3 photoelectron spectroscopy (PES) spectrum of Co measured in coincidence with the L3-VV Auger-electron spectroscopy (AES) peak is analyzed by a many-body theory. The spectrum provides hard evidence that the L3 PES shakeup/off satellite relaxes fully to the L3 PES main line prior to the L3-hole decay. This is in accord with the experimental finding that except for a very weak AES satellite, there is no appreciable line shape change between the singles (noncoincidence) L3-VV AES spectrum of Co measured just above the L3 PES main-line ionization edge and the one far above the L1 -level ionization edge. The delocalization time of the valence hole created together with the core-hole in the atomic L shell in Co is shorter than the core-hole lifetime.
Publication date: 3 June 2013 Source:Chemical Physics, Volume 418 Author(s): ?skender Muz , Murat Ati? , Osman Canko , Erdem Kamil Y?ld?r?m The structure and some electronic properties of neutral and anionic Li5Hn (n=0–6) clusters have been studied by using the stochastic search method with the B3LYP/6-31G level of theory. After searching possible isomers, first few isomers with the lowest energy have been recalculated by the B3LYP/6-311G++(2d,2p) and CCSD(T)/6-311G++(2d,2p) level of theory. The method used in this study has been compared with the previously reported ab initio calculations, and its reliability has been confirmed. The anionic Li5Hn (n=0–6) clusters are reported in this study for the first time. Our results show that in general, stability increases with increasing number of hydrogen atoms. The fragmentation energies of hydrogenated Li5 clusters are easier to fragmentation the two hydrogen atoms than one hydrogen atom in hydrogenated clusters, and it is too high for the reversible hydrogen storage systems.
Publication date: 3 June 2013 Source:Chemical Physics, Volume 418 Author(s): Yajuan Guo , Jianfeng Jia , Xiao-Hua Wang , Ying Ren , Haishun Wu Potassium borohydrides [KBH4] is an attractive candidate for on-board storage because it contains high densities of hydrogen by weight and volume. Using a set of recently developed theoretical first-principles methods, we predict hydrogen storage reactions in the K-M(Li, Na, Ca)-B-H system. Hydrogen release from KBH4 is predicted to proceed via intermediate K2B12H12 phase. In the present study, we predict two new hydrogen storage reactions that are some of the most attractive among the presently known ones. They are predicted to have thermodynamics for hydrogen release within the target window for on-board storage being actively considered for hydrogen storage applications.
Publication date: Available online 7 May 2013 Source:Chemical Physics Author(s): Somedatta Pal , Sanjoy Bandyopadhyay Protein-water interactions and their influence on surrounding water is a long-standing problem. Despite its importance, the origin of differential water behavior at the protein surface is still elusive. We have performed molecular simulations of the protein barstar in aqueous medium. Efforts have been made to explore how the conformational motions of the protein segments in the native form and the heterogeneous electrostatic interactions with the polar and charged groups of the protein affect the interfacial water properties. The calculations reveal that reduced dimension of the hydration layer on freezing the protein’s degrees of freedom does not modify the heterogeneous water distributions around the protein. However, turning off the protein–water electrostatic contribution leads to non-preferential near-uniform water arrangements at the surface. It is further shown that with protein–water electrostatic interactions turned on, the local structuring of water molecules around the segments are correlated with their degree of exposure to the solvent.
Publication date: 16 May 2013 Source:Chemical Physics, Volume 417 Author(s): Alendu Baura , Monoj Kumar Sen , Bidhan Chandra Bag In this paper we have studied the effect of non Markovian thermal bath on the barrier crossing dynamics of a charged particle which is embedded in a non Markovian thermal bath in presence of a constant magnetic field. Based on the Fokker–Planck description of stochastic process in the extended phase space we have calculated barrier crossing rate. It exhibits that the barrier crossing rate for a given magnetic field strength enhances as the thermal bath deviates more from Markovian characteristics by increasing memory time of the dynamics. This may account deviation of experimental result from the Kramer’s rate.
Publication date: Available online 14 May 2013 Source:Chemical Physics Author(s): Raghunathan Ramakrishnan , Shampa Raghunathan , Mathias Nest In this study we present methodological developments of the time-dependent configuration interaction (TDCI) method for ab initio electron dynamics in donor-bridge-acceptor systems. Especially, we investigate the role of valence electron correlation, the scheme for selecting the determinantal basis, and the computational effort. Our test systems are molecules of the type Li-(C2)n-CN, Li-(C2H2)n-CN, and Na9-(C2H2)2-CN. In this way, this study is intended as a step towards rigorous description of charge transfer in molecular wires attached to metal surfaces or nanoparticles using a many-electron wavefunction. Also, a multi-reference configuration interaction singles approach is suggested as a good compromise between computational effort and accuracy.
Publication date: 3 June 2013 Source:Chemical Physics, Volume 418 Author(s): P. Papp , Š. Matej?ík , P. Mach , J. Urban , I. Paidarová , J. Horá?ek The method of analytic continuation in the coupling constant (ACCC) in combination with use of the statistical Padé approximation is applied to the determination of resonance energy and width of some amino acids and formic acid dimer. Standard quantum chemistry codes provide accurate data which can be used for analytic continuation in the coupling constant to obtain the resonance energy and width of organic molecules with a good accuracy. The obtained results are compared with the existing experimental ones.
Publication date: 3 June 2013 Source:Chemical Physics, Volume 418 Author(s): Viviane S. Vaiss , Itamar Borges Jr. , Fernando Wypych , Alexandre A. Leitão DFT calculations with periodic boundary conditions were used to study two formation reaction mechanisms of adsorbed free hydroxide anions on the surface of the brucite, Mg(OH)2. In the first mechanism, we investigated the migration of a hydroxide anion present in the structure of Mg(OH)2 to the layer surface. In the second, a mechanism composed of three elementary reactions was examined for the reaction of H2O molecules with the brucite layer surface. The result in both mechanisms is the formation of hydroxide anions and a hydroxide vacancy in the positively charged Mg(OH)2 layer. The global reaction is the same in both cases and the computed Gibbs free energy variation equals 37.5kcal/mol at room temperature. The reaction barrier for the formation of hydroxide anion on Mg(OH)2 surface from H2O dissociation (27.6kcal/mol) is lower than the reaction barrier for the formation of hydroxide anions from Mg(OH)2 dissociation (43.2kcal/mol).
Publication date: 11 July 2013 Source:Chemical Physics, Volume 420 Author(s): Michael J. Gregory , Mathew Anderson , Timothy P. Causgrove Energy barriers in kinetics are typically determined by measuring the rate as a function of temperature. We have used an alternative and complementary technique, temperature-derivative spectroscopy, to characterize folding of poly-l-glutamic acid in response to a change in pH. After the solution pH is changed photolytically at low temperature (150K) using a photogenerating acid, the solution is warmed while monitoring the helix–coil transition by its infrared absorption. At high initial pH, the secondary structure change occurs at 180K. If the initial pH is near 6, helix formation occurs near 190K. The results are interpreted in terms of the pre-exponential factor and enthalpy barrier for protein folding. Because the pH change is extrinsic to the system under study, this technique enables temperature-derivative spectroscopy to be used with any phenomenon that is pH dependent and with a wide range of spectroscopic measurement techniques.
Publication date: Available online 11 May 2013 Source:Chemical Physics Author(s): Stewart F. Parker , Silvia Imberti , Samantha K. Callear , Peter W. Albers Glassy carbon is a form of carbon made by heating a phenolic resin to high temperature in an inert atmosphere. It has been suggested that it is composed of fullerene-like structures. The aim of the present work was to characterise the material using both structural (neutron diffraction and transmission electron microscopy) and spectroscopic (inelastic neutron scattering, Raman and X-ray photoelectron spectroscopies) methods. We find no evidence to support the suggestion of fullerene-like material being present to a significant extent, rather the model that emerges from all of the techniques is that the material is very like amorphous carbon, consisting of regions of small graphite-like basic structural units of partly stacked but mismatched structure with the edges terminated by hydrogen or hydroxyls. We do find evidence for the presence of a small quantity of water trapped in the network and suggest that this may account for batch-to-batch variation in properties that may occur.
Publication date: Available online 25 April 2013 Source:Chemical Physics Author(s): Camille J. Roche , David Dantsker , Elizabeth R. Heller , Joseph E. Sabat , Joel M. Friedman Hydration waters impact protein dynamics. Dissecting the interplay between hydration waters and dynamics requires a protein that manifests a broad range of dynamics. Proteins in reverse micelles (RMs) have promise as tools to achieve this objective because the water content can be manipulated. Hemoglobin is an appropriate tool with which to probe hydration effects. We describe both a protocol for hemoglobin encapsulation in reverse micelles and a facile method using PEG and cosolvents to manipulate water content. Hydration properties are probed using the water-sensitive fluorescence from Hb bound pyranine and covalently attached Badan. Protein dynamics are probed through ligand recombination traces derived from photodissociated carbonmonoxy hemoglobin on a log scale that exposes the potential role of both ? and ? solvent fluctuations in modulating protein dynamics. The results open the possibility of probing hydration level phenomena in this system using a combination of NMR and optical probes.
Publication date: 11 July 2013 Source:Chemical Physics, Volume 420 Author(s): Aurélien Guy , Anne Bourdon , Marie-Yvonne Perrin A vibrational collisional model based on the database of the University of Bari is used to investigate nonequilibrium phenomena in nitrogen nozzle flows. For the cases studied, the vibrational distribution in the divergent section appeared to significantly deviate from a Boltzmann distribution. Multiquanta Vibration-Translation processes are shown to have a major influence on the recombination of the flow and on the shape of the vibrational distribution along the nozzle axis. Based on these results, a reduced model is derived with n groups of vibrational levels with their own internal temperatures to model the shape of the vibrational distribution. In this model, energy and chemistry source terms are calculated self-consistently from the rate coefficients of the vibrational database. For the studied nozzle flows, a good agreement is observed between the results of the vibrational collisional model with 68 levels and those of the reduced model with only 3 groups of levels.
Publication date: 11 July 2013 Source:Chemical Physics, Volume 420 Author(s): A. Marbeuf , S.F. Matar , P. Négrier , L. Kabalan , J.F. Létard , P. Guionneau The spin crossover properties and the domains of existence of the different phases for the [Fe(PM-BIA)2(NCS)2] complex are obtained from combining DFT and classical molecular dynamics (MD). The potential energy surfaces expressed in the Morse form for Fe–N interactions are deduced from molecular DFT calculations and they allow producing Infra Red and Raman frequencies. These Fe–N potentials inserted in a classical force field lead from MD calculations to the relative energies of the high spin and low spin configurations of the orthorhombic structure. The MD investigations have also allowed assessing the experimental (P,T) phase diagram by showing the monoclinic polymorph in its two spin-states, and generating two triple points.
Publication date: 16 May 2013 Source:Chemical Physics, Volume 417 Author(s): S.H. Reza Shojaei , Filippo Morini , Michael S. Deleuze A comprehensive study of the He (I) ultra-violet photoelectron spectra of fluorene, carbazole and dibenzofuran is presented with the aid of one-particle Green’s Function calculations employing the outer-valence Green’s Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with Dunning’s correlation consistent basis sets of double and triple zeta quality (cc-pVDZ, cc-pVTZ). Extrapolations of the ADC(3) results for the outermost one-electron ?-ionization energies to the cc-pVTZ basis set enable theoretical insights into He (I) measurements within ?0.15eV accuracy, up to the ?-ionization onset. The lower ionization energy of carbazole is the combined result of mesomeric and electronic relaxation effects. OVGF/cc-pVDZ or OVGF/cc-pVTZ pole strengths smaller than 0.85 systematically corroborate a breakdown of the orbital picture of ionization at the ADC(3) level. Comparison is made with calculations of the lowest doublet–doublet excitation energies of the radical cation of fluorene, by means of time-dependent density functional theory (TDDFT).
Publication date: 18 April 2013 Source:Chemical Physics, Volume 416 Author(s): Ankur Saha , Monali N. Kawade , Hari P. Upadhyaya , Awadhesh Kumar , Prakash D. Naik The photodissociation dynamics of 2-bromo-2-chloro-1,1,1-trifluoroethane (halothane) have been studied near 234nm, in a molecular beam environment, employing resonance-enhanced multiphoton ionization with time-of-flight mass spectrometer (REMPI-TOF-MS). Both bromine and chlorine atoms are detected in both the ground and spin–orbit excited states. The C–Br bond scission is observed predominantly due to direct ??(C–Br)?n(Br) transition, with translational energy distribution described with a soft impulsive model. The recoil anisotropy parameter (?) of 0.6±0.2 for this channel vindicates the impulsive nature of dissociation. The diabatic crossing from the n??(C–Br) surface to n??(C–Cl) diabatic surface is responsible for chlorine formation via the C–Cl bond fission, which is supported by the excited state molecular orbital calculations. The velocity distribution of bromine atom has one component, however, that of chlorine atom is bimodal. Both fast and slow chlorine atom channels, with the ? value of 0.3±0.1, are produced impulsively from the n??(C–Cl) repulsive surface.
Graphical abstract
Highlights
? Photodissociation of halothane at 234nm is reported. ? REMPI detection of Br(2P3/2,1/2) and Cl(2P3/2,1/2) fragments; the former channel is predominant. ? The bromine and chlorine fragments have one and two velocity components, respectively. ? Anisotropic distributions of bromine and chlorine fragments observed. ? A diabatic crossing from the n??(C–Br) surface to n??(C–Cl) diabatic surface is responsible for chlorine formation.
Publication date: Available online 1 May 2013 Source:Chemical Physics Author(s): Lucas Kocia , Steve M. Young , Yana A. Kholod , Michael D. Fayer , Mark S. Gordon , Andrew M. Rappe The time-dependent dynamics of phenol dissolved in liquid phenylacetylene is theoretically investigated through first-principles calculations and molecular dynamics. By modeling the hydroxyl functional group with a Morse potential, the bond becomes site-sensitive, vibrating at distinct frequencies when bound at the phenylacetylene triple bond and aromatic ring. This can be exploited to simulate 2D-IR echo spectra using Fourier analysis. The resulting dynamics yields a phenol migration time between the two primary binding sites on phenylacetylene of 3-5 ps in excellent agreement with experiment. Furthermore, this study finds that the mechanism for this migration is strongly influenced by an indirect pathway, in contrast to prior experimental interpretation. The dynamics is found to be primarily dictated by van der Waals forces instead of hydrogen bonding forces, a conclusion that is supported by first principles calculations.
Publication date: 11 July 2013 Source:Chemical Physics, Volume 420 Author(s): G. Aldea-Nunzi , S.W. Chan , K.Y.K. Man , J.M. Nunzi Layer-by-layer (LBL) self-assembling was employed to produce dye-containing multilayer films with a nonlinear optical maleic acid copolymer containing Disperse Red 1 moieties. By alternate adsorption of maleic acid copolymer derivative and polyethyleneimine, films made from 1 to 30 bilayers were prepared and characterized. The effect of salt addition to the polyelectrolyte on the LBL self-assembly process was also studied. Second order optical nonlinearity ?(2) of LBL films was studied by second harmonic generation and its stability was assessed by all-optical poling. A ‘restoring force’ model for the chromophore orientation in the LBL films is proposed to simulate the rotational motion. It clarifies the origin of the stability of the noncentrosymmetry in LBL films.
Publication date: 16 May 2013 Source:Chemical Physics, Volume 417 Author(s): C. Paduani First-principles calculations using density functional theory were performed to study the structure, stability and electronic properties of clusters formed by attaching AlH4 and AlF4 complexes to the Gd atom. The calculated electron affinity of AlH4 is 3.58eV, close to that of chlorine, and for the Gd (AlH4)4 cluster it is 4.95eV, indicative of superhalogen behavior. For AlF4 the calculated electron affinity is 7.36eV, indicating superhalogen behavior. When this complex is used to decorate Gd in number that exceeds its formal valence (+3) the electron affinity increases to 8.42eV in the Gd (AlF4) 4 cluster, which is an indication of hyperhalogen behavior. High-spin ground states are predicted for these moieties, which have same spin multiplicities in both aluminohydrides and aluminofluorides.
Publication date: 16 May 2013 Source:Chemical Physics, Volume 417 Author(s): Jitendra Gupta , P.U. Manohar , Aryya Ghosh , Nayana Vaval , Sourav Pal In this paper, we have presented and analyzed the extended coupled cluster (ECC) energy functional, truncated up to nth perturbation order in which expansion is limit to operators of the single and double excitations. The expression for the first order energy derivatives based on the above truncation schemes has been derived and numerically analyzed. We have done a comparative study for dipole moment in various perturbative ECC (n) methods (2?n?5) for three systems (HF, H2O and BH) at equilibrium geometry. We have particularly studied two variants of ECC (4) and ECC (5?) method for stretched geometry. We have analyzed the contribution of important terms present in ECC functional based on perturbative argument. We have compared our results with standard coupled cluster (CCSD) as well as cubic truncated ECC and also benchmarked with the full CI results wherever available.
Publication date: 18 April 2013 Source:Chemical Physics, Volume 416 Author(s): Genbai Chu , Jun Chen , Fuyi Liu , Xiaobin Shan , Juguang Han , Liusi Sheng The photoionization and photodissociation of oxalyl chloride have been studied by synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry. The ionization energy of C2Cl2O2 (10.91±0.05eV) and appearance energies (AEs) for fragment ions CCl2O+, , CClO+, , , and Cl+ from C2Cl2O2 have been measured from the photoionization efficiency (PIE) spectra. In addition, three conformers of ion, namely trans-, gauche- and cis-conformer are investigated by using CBS-QB3 and W1u methods, which suggest that the existence of the cis-conformation parent ion is consistent with the second onset at 11.6eV in the experimental PIE curve and the associated calculations. The formation channels of fragment ions near the ionization thresholds are discussed by means of CBS-QB3 and W1u calculated results and thermochemistry results. The dominant fragment ion CClO+ is mainly originated from direct cleavage of the elongated C–C bond in the trans-conformer parent ion after ionization. The calculated results are in good agreement with the experimental data.
Graphical abstract
Highlights
? Dissociative photoionization of oxalyl chloride is studied by mass spectrometry. ? The existence of cis-parent ion is attributed to conformational conversion. ? The dominant CClO+ ion mainly originates from direct cleavage after ionization.
Posted on 26 May 2013 | 4:28 am
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