# Chemical Physics

## Current research reports and chronological list of recent articles.

The international scientific journal Chemical Physics welcomes experimental and theoretical papers in the molecular, biological and materials sciences.

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## Chemical Physics - Abstracts

MCTDH study on the reactive scattering of the Cl + HD reaction based on the neural-networks potential energy surface

Publication date: Available online 11 November 2017
Source:Chemical Physics

Author(s): Qingyong Meng

To study the dynamics resonances of the Cl + HD reaction which was proposed to proceed via abstraction mechanism with no clear resonances, we perform dynamics calculations by the multiconfiguration time-dependent Hartree (MCTDH) method based on recently developed neural-networks potential energy surface (Science 347 (2015), 60). The HD molecule in $v = 0$ (GS), $v = 1$ (EX1), $v = 2$ (EX2), and $v = 3$ (EX3) states is used for the reactant. For GS, no distinctive resonance peak is found, while for EX1 two distinctive peaks at kinetics energies of $0.11$ and $0.17$ eV are investigated. These resonance peaks are well consistent with the previous results (Science 347 (2015), 60). Moreover, the present MCTDH calculations predict well-marked resonance peaks at $0.04 , 0.05 , 0.07$, and $0.10$ eV for EX2 and EX3, which indicates that anticipation of the chemical bond softening model (Science 327 (2010), 1501) is confirmed in this work.

Datum: 18.11.2017

Quasirelativistic potential energy curves and transition dipole moments of NaRb

Publication date: Available online 21 October 2017
Source:Chemical Physics

Author(s): M. Wiatr, P. Jasik, T. Kilich, J.E. Sienkiewicz, H. Stoll

We report on extensive calculations of quasi-relativistic potential energy curves and, for the first time, transition dipole moments including spin-orbit and scalar-relativistic effects of the NaRb molecule. The calculated curves of the $0 +$, $0 -$, 1, 2 and 3 molecular states correlate for large internuclear separation with the fourteen lowest atomic energies up to the Na($3 s 2 S 1 / 2$) + Rb($7 s 2 S 1 / 2$) atomic limit. Several new features of the potential energy curves have been found.

Datum: 18.11.2017

Theoretical prediction of noble gas inserted halocarbenes: FNgCX (Ng=Kr, and Xe; X=F, Cl, Br, and I)

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Pragya Chopra, Ayan Ghosh, Banasri Roy, Tapan K. Ghanty

A new series of neutral noble gas inserted compounds involving halocarbenes, mainly, FNgCX (Ng=Kr, and Xe; X=F, Cl, Br, and I) has been predicted through various ab initio quantum chemical techniques such as MP2, DFT, CCSD(T) and MRCI. The structure, stabilities, charge distribution, harmonic vibrational frequencies and topological properties of these compounds have been investigated. It is found that the predicted species are energetically stable with respect to all the plausible 2-body and 3-body dissociation pathways, with the exception of the 2-body channel that leads to the global minimum products (FCX+Ng). Despite this, existence of finite barrier heights indicates that these compounds are kinetically stable with respect to global minimum products. The computational results indicate that it might be possible to prepare and characterize the most stable singlet state of FNgCX molecules under cryogenic conditions through suitable experimental technique(s).

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Datum: 18.11.2017

The effect of site-specific spectral densities on the high-dimensional exciton-vibrational dynamics in the FMO complex

Publication date: 6 November 2017
Source:Chemical Physics, Volume 497

Author(s): Jan Schulze, Mohamed F. Shibl, Mohammed J. Al-Marri, Oliver Kühn

The coupled exciton-vibrational dynamics of a three-site model of the FMO complex is investigated using the Multi-layer Multi-configuration Time-dependent Hartree (ML-MCTDH) approach. Emphasis is put on the effect of the spectral density on the exciton state populations as well as on the vibrational and vibronic non-equilibrium excitations. Models which use either a single or site-specific spectral densities are contrasted to a spectral density adapted from experiment. For the transfer efficiency, the total integrated Huang-Rhys factor is found to be more important than details of the spectral distributions. However, the latter are relevant for the obtained non-equilibrium vibrational and vibronic distributions and thus influence the actual pattern of population relaxation.

Datum: 18.11.2017

Molecular dynamics simulation of the thermosensitivity of the human connexin 26 hemichannel

Publication date: 26 January 2018
Source:Chemical Physics, Volume 500

Connexin hemichannels mediate cytoplasm and extracellular milieu communication by exchanging a variety of cytoplasmic molecules and ions. These hemichannels can be regulated by external stimuli such as mechanical stress, applied voltage, pH and temperature changes. Although there are many studies on structures and functions of connexin 26 in contexts of pH, ion concentration and voltage, employing computational methods, no such study has been performed so far involving temperature changes. In this study, using molecular dynamics simulation, we investigate thermosensitivity of the human Connexin 26 hemichannel. Our results show that the channel approaches a structurally closed state at lower temperature compared to higher temperature. This is in fair agreement with experimental results that indicate channel closure at lower temperature. Furthermore, our MD simulation results show that some regions of connexin 26 hemichannel are more sensitive to temperature compared to other regions. Whereas the intercellular half of the channel does not show any considerable response to temperature during the simulation time accessible in this study, the cytoplasmic half approaches a closed structural state at lower temperature compared to the higher temperature. Specifically, our results suggest that the cytoplasmic loop, the cytoplasmic half of the second transmembrane helix, and the N-terminus helix play a dominant role in temperature gating.

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Datum: 18.11.2017

6.2 μm Spectrum and 6-Dimensional Morphed Potentials of OC-H2O

Publication date: Available online 13 November 2017
Source:Chemical Physics

Author(s): Luis A. Rivera-Rivera, Blake A. McElmurry, Kevin W. Scott, Sean D. Springer, Robert R. Lucchese, John W. Bevan, Igor I. Leonov, Laurent H. Coudert

Rovibrational transitions associated with tunneling states in the ν 5 (water bending) vibration of the OC-H2O complex have been recorded using a supersonic jet mode-hop free quantum cascade laser spectrometer at 6.2 μm. Analysis of the resulting spectra is facilitated by incorporating fits of previously recorded microwave and submillimeter data accounting for Coriolis coupling. The theoretical basis of morphing a 5-D frozen monomers potential was initially developed and then extended to two 6-D morphed potentials. A combination of these spectroscopic results and previous rovibrational data for the ν 5 vibration in OC-D2O are then used to generate a 6-D morphed potential surface for the intermolecular and the water bending vibrations. An alternative 6-D morphed potential of the intermolecular and the ν 3 (CO stretching) vibrations was also generated. These determined morphed potentials then formed the basis for modeling the dynamics of the complex and prediction of accurate intermolecular rovibrational frequencies of the complex.

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Datum: 18.11.2017

Two types of coherence resonance in an intracellular calcium oscillation system

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): Juan Ma, Qingyu Gao

Two types of noise induced oscillations (NIOs) near Hopf bifurcation and coherence resonance (CR) have been studied analytically in a calcium system. One is NIOs with small amplitude and internal signal stochastic resonance (CR type I) occurs, and the other is noise induced spike and the regularity of which reaches a maximum at an optimal noise level (CR type II). For the first type, stochastic normal form theory is employed to analyze the signal to noise ratio of the NIOs depending on the noise intensity. For the second type, based on the independent assumption, activation time and excursion time have been split, and the sum of which reach a minimum with the variation of noise intensity. The theoretical evidence is also explained in detail. Numerical simulations show good agreements with the theoretical results. It may indicate some kind of transmit mechanism involved in stochastic calcium dynamics.

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Datum: 18.11.2017

Contents

Publication date: 6 November 2017
Source:Chemical Physics, Volume 497

Datum: 18.11.2017

Excited state properties of 2′-hydroxychalcone analogues functionalized with a diene moiety studied by steady state and laser flash photolysis

Publication date: 26 January 2018
Source:Chemical Physics, Volume 500

Author(s): Yukino Shinozaki, Minoru Yamaji, Tatsuo Arai

2′-Hydroxychalcone (HC) analogues 1 and 2 having a diene part tethering the phenyl and naphthyl chromophores, respectively, were prepared, and their photochemical and photophysical properties were studied. Fluorescence from these compounds was absent in solution and the solid state. Based on the results obtained upon steady state and laser flash photolyses, compound 2 was found to be substantially stable on photoirradiation without undergoing intersystem crossing to the triplet state whereas compounds 1 showed transient absorption due to the triplet tautomer. The deactivation processes in the excited states were discussed by considering energetic reaction diagrams for the corresponding tautomers and isomers.

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Datum: 18.11.2017

The effect of varied pH on the luminescence characteristics of antibody–mercaptoacetic acid conjugated ZnS nanowires

Publication date: 6 November 2017
Source:Chemical Physics, Volume 497

Author(s): Madeeha Chaudhry, Malik Abdul Rehman, Asghari Gul, Raheel Qamar, Arshad Saleem Bhatti

We demonstrate here that the effect of varied pH of the media on the photoluminescence (PL) properties of mercaptoacetic acid (MAA) and digoxin antibody (Ab) conjugated zinc sulphide (ZnS) nanowires. The charge-transfer kinetics from MAA to ZnS and vice versa showed a profound effect on the luminescence of ZnS defect states. The PL intensity of the ZnS defect states showed strong dependence on the value of pH with respect to the pKa of MAA. The carboxyl and thiol group of MAA in the protonated (pH&lt;pKa) and deprotonated (pH&gt;pKa) states resulted in the quenched PL intensity. While for pHpKa, the PL intensity was regained as there was equal probability of both protonated and deprotonated carboxyl and thiol groups. These findings indicated that pH of the environment is a key parameter for the use of MAA-Ab conjugated ZnS nanowires as an optical biomarker.

Datum: 18.11.2017

Contents

Publication date: 17 October 2017
Source:Chemical Physics, Volume 496

Datum: 18.11.2017

Modeling the THF clathrate hydrate dynamics by combining molecular dynamics and quasi-elastic neutron scattering

Publication date: 17 October 2017
Source:Chemical Physics, Volume 496

Author(s): Eric Pefoute, Ludovic Martin-Gondre, Jacques Ollivier, Jean-Christophe Soetens, Margarita Russina, Arnaud Desmedt

The dynamics of the THF molecule encapsulated in the type II clathrate hydrate matches the MD-QENS observation time (typically 0.1–10ps) between 100K and 270K. Spatial and time characteristics of the THF molecule’s dynamics obtained by means of MD simulations are in agreement with those experimentally determined by means of quasielastic neutron scattering. A detailed model of the THF dynamics is then proposed through the calculations of MD-derived properties. Reorientational relaxation has been observed on a timescale of 0.7±0.1ps at 270K with activation energy of 3.0±0.3kJ/mol in addition to a highly damped rotational excitation occurring in the plane of the THF molecule with a period of ca. 2ps. Moreover, the anisotropic cage energy landscape of the THF clathrate hydrate is revealed through a comprehensive investigation of THF orientational distribution functions, revealing the occurrence of preferred orientation of the THF molecule within the cage.

Datum: 18.11.2017

IFC (Editorial Board)

Publication date: 24 November 2017
Source:Chemical Physics, Volumes 498–499

Datum: 18.11.2017

Binding affinity of the L-742,001 inhibitor to the endonuclease domain of A/H1N1/PA influenza virus variants: Molecular simulation approaches

Publication date: Available online 11 November 2017
Source:Chemical Physics

Author(s): Hung Nguyen, Hoang Linh Nguyen, Huynh Quang Linh, Minh Tho Nguyen

The steered molecular dynamics (SMD), molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) and free energy perturbation (FEP) methods were used to determine the binding affinity of the L-742,001 inhibitor to the endonuclease domain of the A/H1N1/PA influenza viruses (including wild type (WT) and three mutations I79L, E119D and F105S for both pH1N1 PA and PR8 PA viruses). Calculated results showed that the L-742,001 inhibitor not only binds to the PR8 PAs (1934 A influenza virus) better than to the pH1N1 PAs (2009 A influenza virus) but also more strongly interacts with the WT endonuclease domain than with three mutant variants for both pH1N1 PA and PR8 PA viruses. The binding affinities obtained by the SMD, MM-PBSA and FEP methods attain high correlation with available experimental data. Here the FEP method appears to provide a more accurate determination of the binding affinity than the SMD and MM-PBSA counterparts.

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Datum: 18.11.2017

Vibrational spectroscopy modeling of a drug in molecular solvents and enzymes

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): Christian J. Devereux, Kristen D. Fulfer, Xiaoliu Zhang, Daniel G. Kuroda

Modeling of drugs in enzymes is of immensurable value to many areas of science. We present a theoretical study on the vibrational spectroscopy of Rilpivirine, a HIV reverse transcriptase inhibitor, in conventional solvents and in clinically relevant enzymes. The study is based on vibrational spectroscopy modeling of the drug using molecular dynamics simulations, DFT frequency maps, and theory. The modeling of the infrared lineshape shows good agreement with experimental data for the drug in molecular solvents where the local environment motions define the vibrational band lineshape. On the other hand, the theoretical description of the drug in the different enzymes does not match previous experimental findings indicating that the utilized methodology might not apply to heterogeneous environments. Our findings show that the lack of reproducibility might be associated with the development of the frequency map which does not contain all of the possible interactions observed in such systems.

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Datum: 18.11.2017

IFC (Editorial Board)

Publication date: 6 November 2017
Source:Chemical Physics, Volume 497

Datum: 18.11.2017

Contents

Publication date: 24 November 2017
Source:Chemical Physics, Volumes 498–499

Datum: 18.11.2017

Probing adsorption sites of carbon dioxide in metal organic framework of [Zn(bdc)(dpds)]n: A molecular simulation study

Publication date: 6 November 2017
Source:Chemical Physics, Volume 497

Author(s): Shih-I Lu, Jian-Min Liao, Xiao-Zhuang Huang, Chia-Hsun Lin, Szu-Yu Ke, Chih-Chieh Wang

We used force-field based grand-canonical Monte Carlo simulation method and density functional theory to study adsorption characteristics of carbon dioxide (CO2) molecules in a metal-organic framework (MOF) compound, [Zn(bdc)(dpds)]n. The studied MOF include a metal ion (Zn(II)), an anion organic linker (dianion of benzene dicarboxylicacid, bdc2−) and a neutral organic linker (4,4′-dipyridyldisulfide, dpds). Results from calculated adsorption isotherms and enthalpies of adsorption agree with the experimental data. The interactions between the adsorbed CO2 and the organic linkers were examined in simulations. Calculated results show available absorption sites are surrounded by two dpds ligands in which an S-S bond as an N-N′ spacer connect two pyridines. In contrast, the bdc2− ligand does not give a significant contribution to the substantial adsorption amount even though it contains the carboxylate group that provides available bonding site to CO2.

Datum: 18.11.2017

IFC (Editorial Board)

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Datum: 18.11.2017

Effects of adding LiBF4 on the glass-transition kinetics of 1,2-propanediol

Publication date: 6 November 2017
Source:Chemical Physics, Volume 497

Author(s): Yukio Terashima, Kiyoshi Takeda

By applying an isoconversional method to differential-scanning calorimetry (DSC) data, we have discovered that the addition of LiBF4 significantly affects the activation energy Eα of the glass transition of 1,2-propanediol. Depending upon its concentration, the dynamics of the glass transition are affected more by adding LiBF4 at an early stage of the glass-to-liquid transition rather than at later stages. As the mole fraction x of LiBF4 increases, the value of Eα initially increases, but it decreases dramatically during the glass transition. The abrupt decline in Eα suggests that the addition of LiBF4 breaks cooperative rearranging motions into smaller parts. The expansion of cooperativity, and its fragmentation with increasing temperature, can be explained in terms of competition between the hydrogen-bond networks of the alcohol solvent and the ionic interactions due to the added salt. The variability of Eα with temperature is found to correlate exponentially with the dynamic fragility.

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Datum: 18.11.2017

Predictive methods of some optoelectronic properties for blends based on quaternized polysulfones

Publication date: 24 November 2017
Source:Chemical Physics, Volumes 498–499

Author(s): Adina Maria Dobos, Anca Filimon

Blends based on quaternized polysulfones were investigated in terms of optical and electronic properties. By applying the Bicerano formalism the refractive index and dielectric constant were evaluated. Also, the dielectric constant of these blends was studied as a function of temperature and frequency. As the result of the main chain structure and charged groups, an increase in theoretical values of the refractive index and dielectric constant with increasing of the ionic quaternized units content in the polymer blend occurs. Additionally, decrease in the dielectric constant with the increase of frequency and decrease of temperature was observed. Refractive index and dielectric constant values indicate that the analyzed samples are transparent and can be used in obtaining of materials with applications involving a small polarizability. Thus, the results are important in prediction of the special optoelectronic features of new polymers blends to obtain high-performance materials with applications in electronic and biomedical fields.

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Datum: 18.11.2017

A multimode-like scheme for selecting the centers of Gaussian basis functions when computing vibrational spectra

Publication date: Available online 23 October 2017
Source:Chemical Physics

Author(s): Sergei Manzhos, Xiaogang Wang, Tucker Carrington

We compute vibrational energy levels using Gaussian basis functions whose centers are in slabs that include the lower-dimensional hyperplanes on which the Multimode approximation to the potential is based. We use more potential points than basis functions to increase the accuracy. The number of Gaussian basis functions is smaller than the number required using the best existing methods. For formaldehyde, the first 50/100 levels we compute, using 30,000 Gaussians and 120,000 points, in 4D-like slabs, differ from numerically exact levels by 0.3/0.6 cm−1 (mean absolute error). With 3D-like slabs, the mae for the first 50/100 levels is 0.17/0.47 cm−1 with 30,000 basis functions and 0.95/2.06 cm−1 with 20,000 basis functions. Although we use a multimode-like idea to select Gaussian centers, we use a single point set and there is no need to write the potential in multimode form and no need to neglect high-order terms.

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Datum: 18.11.2017

Publication date: 26 January 2018
Source:Chemical Physics, Volume 500

Author(s): Martina Zámečníková, Pavel Soldán

Radiative lifetimes of the ro-vibrational bound states of $HeLi +$($b 3 ∑ +$) are calculated quantum-mechanically when both bound-bound and bound-free processes are taken into account. The calculations are restricted to the initial states with low rotational quantum numbers. For the rotationless molecular ion, the shortest lifetime is $1.30 × 10 - 6 s$ of the ground vibrational state. With increasing vibration excitations the radiative lifetimes slightly increase, but keep below $10 - 5 s$ for the next 17 vibrational states, then they start to increase more rapidly up to $2.41 × 10 - 2 s$ for the highest vibrational state. The radiative lifetimes also tend to slightly prolong with increasing rotational excitations but stay on the same magnitude for the low rotational quantum numbers.

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Datum: 18.11.2017

Dynamic interference in the resonance-enhanced multiphoton ionization of hydrogen atoms by short and intense laser pulses

Publication date: Available online 21 October 2017
Source:Chemical Physics

Author(s): Anne D. Müller, Eric Kutscher, Anton N. Artemyev, Lorenz S. Cederbaum, Philipp V. Demekhin

Photoionization of the hydrogen atom by intense and short coherent laser pulses is investigated from first principles by a numerical solution of the time-dependent Schrödinger equation in the dipole-velocity gauge. The considered photon energies are resonant to the $1 s → 2 p$ excitation, and the pulse intensities are high enough to induce Rabi floppings. The computed resonance-enhanced two-photon ionization spectra as well as the three-photon above threshold ionization spectra exhibit pronounced multiple-peak patterns due to dynamic interference. Fingerprints of dynamic interference can also be seen directly in the radial density of the photoelectron. The impact of the variation of the pulse intensity and photon energy on the dynamic interference is investigated, and the angular distribution of the emitted electrons is analyzed in some details. The present precise numerical results confirm our previous theoretical predictions on the two-photon ionization spectra (Demekhin and Cederbaum, 2012) made within a minimal few-level model.

Datum: 18.11.2017

183W nuclear dipole moment determined by gas-phase NMR spectroscopy

Publication date: 24 November 2017
Source:Chemical Physics, Volumes 498–499

Author(s): Piotr Garbacz, Włodzimierz Makulski

The magnetic dipole moment of the tungsten-183 nucleus, µ(183W), is determined from measurements of gas-phase 183W nuclear magnetic resonance of tungsten hexafluoride dissolved in CF4. The tungsten-183 resonance frequency combined with recently reported computations of the magnetic shielding of the 183W nucleus in WF6 (Ruud et al., 2014) yields μ(183W) = 0.116953(18) μN. Moreover, it is found that the gas-to-liquid shifts of nuclear shielding for WF6 are ΔσGL(19F) = −6.9 ppm and ΔσGL(183W) = −18.4 ppm. The spin–spin coupling 1 J(183W,19F) is 43.75(24) Hz for liquid WF6.

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Datum: 18.11.2017

IFC (Editorial Board)

Publication date: 17 October 2017
Source:Chemical Physics, Volume 496

Datum: 18.11.2017

IR induced photochemistry of glycolaldehyde in nitrogen matrix

Publication date: 17 October 2017
Source:Chemical Physics, Volume 496

Author(s): Fabrice Duvernay, Teddy Butscher, Thierry Chiavassa, Stephane Coussan

The conformational equilibria and IR isomerisation processes of glycolaldehyde (HOCH2CHO) conformers have been studied at low temperature in nitrogen cryogenic matrix. The effects of selective IR irradiation, in the $ν OH$ and $ν CH$ domains, have been followed by FTIR spectroscopy. After deposition the main form is the most stable one, CC (Cis-Cis), which features an intramolecular hydrogen bond. Upon selective IR irradiation, this latter form is able to interconvert into two open forms, those called TT (Trans–Trans), and TG (Trans-Gauche). From TT and TG forms, no recovering (by tunneling, dark process, irradiation, annealing, etc.) of the initial state (i.e. CC regeneration) has been observed. However, a TTTG thermal equilibrium is observed with a standard reaction enthalpy about 0.37kJmol−1.

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Datum: 18.11.2017

Cluster formation and percolation in ethanol-water mixtures

Publication date: 17 October 2017
Source:Chemical Physics, Volume 496

Author(s): Orsolya Gereben, László Pusztai

Results of systematic molecular dynamics studies of ethanol-water mixtures, over the entire concentration range, were reported previously that agree with experimental X-ray diffraction data. These simulated systems are analyzed in this work to examine cluster formation and percolation, using four different hydrogen bond definitions. Percolation analyses revealed that each mixture (even the one containing 80mol% ethanol) is above the 3D percolation threshold, with fractal dimensions, df , between 2.6 and 2.9, depending on concentration. Monotype water cluster formation was also studied in the mixtures: 3D water percolation can be found in systems with less than 40mol% ethanol, with fractal dimensions between 2.53 and 2.84. These observations can be put in parallel with experimental data on some thermodynamic quantities, such as the excess partial molar enthalpy and entropy.

Datum: 18.11.2017

Controlling harmonic distributions from H2+ driven by linearly and circularly polarized laser fields

Publication date: 24 November 2017
Source:Chemical Physics, Volumes 498–499

Author(s): Liqiang Feng, Yi Li, Hang Liu

The spatial distributions of the high-order harmonics from H2 + driven by the linearly and the circularly polarized laser fields have been theoretically investigated. It is found that when the molecular axis parallels to the polarized direction of the linearly polarized laser field, the contributions of the harmonics are mainly from the negative-H and the positive-H for the cases of E(t) &gt; 0 and E(t) &lt; 0, respectively. As the angle between the molecular axis and the linearly polarized laser field increases, the contributions of the harmonics from the negative-H are enhanced and play the main role in the harmonic spectrum. Further, with the introduction of the controlling circularly polarized laser field, the intensity enhancement of the harmonics from the positive-H can be achieved. Moreover, the contributions of the harmonics from the two-H nuclei are sensitive to the ellipticity of the laser field. Finally, the time–frequency analyses of the harmonics and the time-dependent electron locations have been given to explain the physical mechanism behind the spatial distributions of the harmonics from the two-H nuclei of H2 +.

Datum: 18.11.2017

First-principles investigation of decomposition and adsorption properties of RDX on the surface of MgH2

Publication date: 17 October 2017
Source:Chemical Physics, Volume 496

Author(s): Guo-Ning Rao, Miao Yao, Jin-Hua Peng

Surface adsorption and decomposition mechanisms of cyclotrimethylenetrinitramine (RDX) molecules on the MgH2 (110) crystal face are investigated in this paper by employing the First-Principles. With the N-NO2 bond of RDX molecules asa reference, 12 adsorption sites are considered that are vertical (V1-V6) and parallel (P1-P6) to the MgH2 (110) surface. Results show that these 12 types of adsorption of RDX molecules on the MgH2 (110) crystal face are all chemical adsorption with high heat release, where the vertical Mg-top position (V1) is the most stable adsorption configuration. In all the 12 types of chemical adsorption, RDX molecules are decomposed, through 4 mechanisms including bis-nitro mono-N-O bond rupture, mono-nitro mono-N-O bond rupture, mono-nitro bis-N-O bond rupture and mono-N-O2 bond rupture, where the V-type adsorption is due to N-O bond rupture and the P-type adsorption is due to N-NO2 bond rupture, resulting in RDX decomposition. Secondly, in proximity to the Fermi level, the density of states of the RDX molecule highly coincides with that of the MgH2 (110) crystal face, which is prone to cause orbital hybridization and RDX decomposition. Also, the density of states in proximity to the Fermi level is mainly contributed by nitro O atoms and ring N atoms of RDX, as well asMg atoms of the MgH2 (110) crystal face, and these 3 types of atoms are also active centers for chemical adsorption and decomposition reaction. Finally, an obvious phenomenon of charge transfer is present between Mg atoms in the first layer of the MgH2 (110) crystal face and O atoms in the nitro group of RDX. Also, the charge change in O and Mg atoms in the V configuration is greater than that in the P configuration, indicating that the V configuration has stronger interaction between RDX and the MgH2 (110) crystal face, and thus RDX in the V configuration is more prone to decomposition and the V configuration represents a better adsorption mode.

Datum: 18.11.2017

IFC (Editorial Board)

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Datum: 18.11.2017

A quantum dynamical study of the photoelectron spectra and the Renner-Teller effect in BrCN and ClCN based on four-component potential energy hypersurfaces

Publication date: Available online 12 October 2017
Source:Chemical Physics

Author(s): V.A. Tran, M. Pernpointner

In this work we investigate the Renner-Teller effect (RTE) in the photoelectron spectra of ClCN and BrCN. The spectra were calculated by a nuclear wave packet propagation on coupled cationic $Π 1 / 2 / Π 3 / 2$ surfaces obtained by the four-component Fock-space coupled cluster method. The scalar relativistic, spin-orbit and electron correlation effects are consistently included in the hypersurfaces for the three internal nuclear degrees of freedom. In contrast to other approaches no coupling matrix elements involving the spin-orbit operator together with an explicit representation of the wave function were necessary. The current study extends earlier work on the RTE for the derivation of the Renner-Teller parameters c and d where only one nuclear degree of freedom was considered (Pernpointner and Salopiata, 2013). The outlined procedure is especially useful for electronic structure methods that yield accurate energies but do not provide an explicit wave function representation.

Datum: 18.11.2017

Adsorption of ethylene carbonate on lithium cobalt oxide thin films: A synchrotron-based spectroscopic study of the surface chemistry

Publication date: 24 November 2017
Source:Chemical Physics, Volumes 498–499

Author(s): Mathias Fingerle, Thomas Späth, Natalia Schulz, René Hausbrand

The surface chemistry of cathodic lithium cobalt oxide (LiCoO2) in contact with the Li-ion battery solvent ethylene carbonate (EC) was studied via synchrotron based soft X-ray photoelectron spectroscopy (SXPS). By stepwise in-situ adsorption of EC onto an rf-magnetron sputtered LiCoO2 thin film and consecutive recording of SXPS spectra, the chemical and electronic properties of the interface were determined. EC partially decomposes and forms a predominantly organic adlayer. Prolonged exposure results in the formation of a condensed EC layer, demonstrating that the decomposition layer has passivating properties. Lithium ions deintercalate from the electrode and are dissolved in the adsorbate phase, without forming a large amount of Li-containing reaction products, indicating that electrolyte reduction remains limited. Due to a large offset between the LiCoO2 valence band and the EC HOMO, oxidation of EC molecules is unlikely, and should require energy level shifts due to interaction or double layer effects for real systems.

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Datum: 18.11.2017

Contents

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Datum: 18.11.2017

About mobility thickness dependence in molecularly doped polymers

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): A.P. Tyutnev, D.S. Weiss, V.S. Saenko, E.D. Pozhidaev

We have investigated the dependence of hole mobility on thickness in free-standing films of bisphenol-A-polycarbonate (PC) doped with 30wt% p-diethylaminobenzaldehyde diphenylhydrazone (DEH). Carrier generation in a time-of-flight (TOF) experiment was achieved through direct ionization of dopant molecules by electron impact using an electron gun supplying pulses of monoenergetic electrons in the range of 2–50keV. The position of dopant ionization depends upon the electron energy and three TOF variants have been recently developed and used in this study. We have found that the hole mobility generally decreased with increasing film thickness with concomitant acceleration of the post-flight current decay indicating that the transport process approaches the steady-state regime, this process happening slightly faster than our model predicts. Numerical calculations have been compared with experimental data. The results are discussed in detail. The way to reconcile ostensibly contradictory interpretations of our results and those commonly reported in literature relying on photo injection technique has been proposed.

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Datum: 18.11.2017

Adsorption of O, O2 and CO on iridium clusters and the investigations of their stability

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): Muna Tayyem, Bothina Hamad, Beate Paulus

Density functional theory calculations were performed to study the stability of Irn clusters as well as the adsorption of O, O2 and CO adsorbates on selected structures. The clusters form three dimensional structures for n&gt;4. Larger clusters of n&gt;13 exhibit simple cubic structures up to n around 32, beyond which fcc structures become more favorable. The binding energy is found to increase as a function of cluster size to approach bulk cohesive energy asymptotically. The total magnetic moment is found to decrease as a function of the cluster size approaching the bulk nonmagnetic ground state. The top adsorption site is the most site of O, O2 and CO on small clusters, unlike Ir64 that exhibits hollow, bridge and top sites, respectively. The vibrational frequencies of CO (O2) on Ir2 and Ir4 are found to be less than those of free molecules of 2102.82 (1562.08)cm−1.

Datum: 18.11.2017

Multimodal hyperspectral optical microscopy

Publication date: 24 November 2017
Source:Chemical Physics, Volumes 498–499

Author(s): Irina V. Novikova, Chuck R. Smallwood, Yu Gong, Dehong Hu, Leif Hendricks, James E. Evans, Ashish Bhattarai, Wayne P. Hess, Patrick Z. El-Khoury

We describe a unique approach to hyperspectral optical microscopy, herein achieved by coupling a hyperspectral imager to various optical microscopes. Hyperspectral fluorescence micrographs of isolated fluorescent beads are first employed to ensure spectral calibration of our detector and to gauge the attainable spatial resolution of our measurements. Different science applications of our instrument are then described. Spatially over-sampled absorption spectroscopy of a single lipid (18:1 Liss Rhod PE) layer reveals that optical densities on the order of 10−3 can be resolved by spatially averaging the recorded optical signatures. This is followed by three applications in the general areas of plasmonics and bioimaging. Notably, we deploy hyperspectral absorption microscopy to identify and image pigments within a simple biological system, namely, a single live Tisochrysis lutea cell. Overall, this work paves the way for multimodal spectral imaging measurements spanning the realms of several scientific disciplines.

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Datum: 18.11.2017

Benzophenone as a photoprobe of polymer films

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): Peter P. Levin, Alexei F. Efremkin, Igor V. Khudyakov

The review article is devoted to kinetics of fast reactions following photoexcitation of benzophenone in polymer films. We observed three processes by ns laser flash photolysis in elastomers: (i) decay of a triple state of benzophenone with hydrogen abstraction from polymer matrix, (ii) formation and decay of geminate radical pairs, (iii) cross-termination of the formed radicals in the polymer bulk. Application of external magnetic field (MF) of B =0.2T essentially affects recombination of geminate (G-) and a bimolecular recombination of free radicals, which escaped polymer cage (F-pairs). Theoretical calculation of MF effects on G- and F-pairs is in agreement with corresponding experimental data. Elongation of elastomer leads to an unexpected observation: recombination in the bulk becomes slower. An explanation of this phenomenon based on elastomer free volume Vf approach was suggested.

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Datum: 18.11.2017

Simultaneous effects of pressure and temperature on the optical transition energies in a Ga0.7In0.3N/GaN quantum ring

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): K. Jaya Bala, A. John Peter, Chang Woo Lee

Simultaneous effects of pressure and temperature on electronic and optical properties are studied in a Ga0.7In0.3N/GaN quantum ring using variational formulism. The changes in exciton binding energy due to the applications of hydrostatic pressure and temperature are obtained taking into account the geometrical confinement. The transition energies of interband and intersubband as a function of hydrostatic pressure, at a constant temperature, are obtained. The oscillator strength due to interband and intersubband optical transitions with the combined effects of hydrostatic pressure and temperature is found. The pressure and temperature induced absorption coefficients as a function of photon energy are investigated in a Ga0.7In0.3N/GaN quantum ring. The results show that the application of pressure leads to blue shift of the resonant peaks of the optical transition whereas the effect of temperature suffers red shift of the resonant peaks.

Datum: 18.11.2017

Investigation on electronic properties of functionalized arsenene nanoribbon and nanotubes: A first-principles study

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): V. Nagarajan, R. Chandiramouli

The electronic properties of arsenene nanotubes and nanoribbons with hydrogenation along the zigzag and armchair edges are studied using density functional theory (DFT) technique. The structural stability of hydrogenated zigzag and armchair arsenene nanostructures are confirmed with formation energy. The electronic properties of arsenene nano-conformers are described in terms of energy band structure and projected density of states spectrum. Furthermore, owing to the influence of hydrogen passivation, buckled orientation and width of arsenene nanostructures, the band gap widens in the range of 0.38–1.13eV. The findings of the present work confirm that the electronic properties of arsenene nanomaterial, can be fine-tuned with the influence of passivation with hydrogen, zigzag or armchair border shapes and effect of the width of nanoribbons or nanotubes, which can be utilized as spintronic device and chemical sensor.

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Datum: 18.11.2017

Predicting Glass-to-Glass and Liquid-to-Liquid Phase Transitions in Supercooled Water using Classical Nucleation Theory

Publication date: Available online 13 November 2017
Source:Chemical Physics

Author(s): Robert F. Tournier

Glass-to-glass and liquid-to-liquid phase transitions are observed in bulk and confined water, with or without applied pressure. They result from the competition of two liquid phases separated by an enthalpy difference depending on temperature. The classical nucleation equation of these phases is completed by this quantity existing at all temperatures, a pressure contribution, and an enthalpy excess. This equation leads to two homogeneous nucleation temperatures in each liquid phase; the first one (Tn- below Tm) being the formation temperature of an “ordered” liquid phase and the second one corresponding to the overheating temperature (Tn+ above Tm). Thermodynamic properties, double glass transition temperatures, sharp enthalpy and volume changes are predicted in agreement with experimental results. The first-order transition line at TLL=0.833×Tm between fragile and strong liquids joins two critical points. Glass phase above Tg becomes “ordered” liquid phase disappearing at TLL at low pressure and at Tn+=1.302×Tm at high pressure.

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Datum: 18.11.2017

Molecular dynamics simulation study of hydration of uranyl nitrate in supercritical water: Dissecting the effect of uranyl ion concentration from solvent density

Publication date: 27 September 2017
Source:Chemical Physics, Volume 495

Author(s): Manish Chopra, Niharendu Choudhury

All atom molecular dynamics simulations of uranyl ions in supercritical water are used to dissect the effects of concentration of uranyl ions and density of water on various structural and dynamic properties of the solutions. The analyses of radial distribution functions as a function of concentration of the uranyl ion and water density reveal that the effect of the former on the local structure is negligible as compared to the same of the later. The number of hydration water of the uranyl ion has been observed to increase with increasing density of the water, but it decreases with the increasing concentration of the uranyl ions. The orientational distributions are observed to be independent of variation in concentration of the uranyl ion, same as the case was with water density. The translational and rotational dynamics of the water molecules have been investigated from the respective mean squared displacements and time correlation functions. Although increase of both the concentration of the uranyl ions and the density of water reduces translational diffusivity of water as well as uranyl ions, the effect of changing water density is more than that of uranyl concentrations. However, orientational relaxation of various molecular vectors of the water molecule is practically unchanged with any variation in concentration of the uranyl ions and it changes only slightly with the change in water density. Unlike at ambient condition, orientational dynamics at supercritical conditions remains virtually unchanged with the change in uranyl ion concentration.

Datum: 18.11.2017

Electronic structures and population dynamics of excited states of xanthione and its derivatives

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Roman G. Fedunov, Marina V. Rogozina, Svetlana S. Khokhlova, Anatoly I. Ivanov, Sergei A. Tikhomirov, Stanislav L. Bondarev, Tamara F. Raichenok, Oleg V. Buganov, Vyacheslav K. Olkhovik, Dmitrii A. Vasilevskii

A new compound, 1,3-dimethoxy xanthione (DXT), has been synthesized and its absorption (stationary and transient) and luminescence spectra have been measured in n-hexane and compared with xanthione (XT) spectra. The pronounced broadening of xanthione vibronic absorption band related to the electronic transition to the second singlet excited state has been observed. Distinctions between the spectra of xanthione and its methoxy derivatives are discussed. Quantum chemical calculations of these compounds in the ground and excited electronic states have been accomplished to clarify the nature of electronic spectra changes due to modification of xanthione by methoxy groups. Appearance of a new absorption band of DXT caused by symmetry changes has been discussed. Calculations of the second excited state structure of xanthione and its methoxy derivatives confirm noticeable charge transfer (about 0.1 of the charge of an electron) from the methoxy group to thiocarbonyl group. Fitting of the transient spectra of XT and DXT has been fulfilled and the time constants of internal conversion $S 2 → S 1$ and intersystem crossing $S 1 → T 1$ have been determined. A considerable difference between the time constants of internal conversion $S 2 → S 1$ in XT and DXT is uncovered.

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Datum: 18.11.2017

Contents

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Datum: 18.11.2017

Concerted-asynchronous reaction path of the excited-state double proton transfer in the 7-azaindole homodimer and 6H-indolo[2,3-b]quinoline/7-azaindole heterodimer

Publication date: Available online 13 November 2017
Source:Chemical Physics

Author(s): Shohei Yamazaki

Reaction path of the excited-state double proton transfer (ESDPT) in the homodimer of 7-azaindole (7AI2 homodimer) and heterodimer of 6H-indolo[2,3-b]quinoline and 7-azaindole (6HIQ-7AI heterodimer) is computationally studied by means of intrinsic reaction coordinate (IRC) calculations. The IRC path determined at the TDDFT level predicts the concerted-asynchronous mechanism for the ESDPT in 6HIQ-7AI as well as in 7AI2, where the N-H$⋯$N hydrogen bonds exhibit asymmetric structures along the reaction path with a single energy barrier. The IRC calculations at the CIS level, however, exhibits a local minimum for single-proton-transferred intermediate, suggesting the stepwise mechanism. Single-point energy calculations at the RI-CC2 level reproduce the TDDFT results, but do not the CIS results. On the basis of potential-energy profiles calculated against intermolecular distance, the discrepancy between the TDDFT and CIS methods is likely attributed to the underestimation of intermolecular interaction energy in the latter method due to the lack of dynamical electron correlation.

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Datum: 18.11.2017

A test of the significance of intermolecular vibrational coupling in isotopic fractionation

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Michael F. Herman, Robert P. Currier, Travis B. Peery, Samuel M. Clegg

Intermolecular coupling of dipole moments is studied for a model system consisting of two diatomic molecules (AB monomers) arranged co-linearly and which can form non-covalently bound dimers.The dipolar coupling is a function of the bond length in each molecule as well as of the distance between the centers-of-mass of the two molecules. The calculations show that intermolecular coupling of the vibrations results in an isotope-dependent modification of the AB-AB intermolecular potential. This in turn alters the energies of the low-lying bound states of the dimers, producing isotope-dependent changes in the AB-AB dimer partition function. Explicit inclusion of intermolecular vibrational coupling then changes the predicted gas-dimer isotopic fractionation. In addition, a mass dependence in the intermolecular potential can also result in changes in the number of bound dimer states in an equilibrium mixture. This in turn leads to a significant dimer population shift in the model monomer-dimer equilibrium system considered here. The results suggest that intermolecular coupling terms should be considered when probing the origins of isotopic fractionation.

Datum: 18.11.2017

Irreversible thermodynamic analysis and application for molecular heat engines

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Umberto Lucia, Emin Açıkkalp

Is there a link between the macroscopic approach to irreversibility and microscopic behaviour of the systems? Consumption of free energy keeps the system away from a stable equilibrium. Entropy generation results from the redistribution of energy, momentum, mass and charge. This concept represents the essence of the thermodynamic approach to irreversibility. Irreversibility is the result of the interaction between systems and their environment. The aim of this paper is to determine lost works in a molecular engine and compare results with macro (classical) heat engines. Firstly, irreversible thermodynamics are reviewed for macro and molecular cycles. Secondly, irreversible thermodynamics approaches are applied for a quantum heat engine with -1/2 spin system. Finally, lost works are determined for considered system and results show that macro and molecular heat engines obey same limitations. Moreover, a quantum thermodynamic approach is suggested in order to explain the results previously obtained from an atomic viewpoint.

Datum: 18.11.2017

A statistical mechanics investigation about general aspects of wetting transition occurring in nonpolar neutral molecule system with a smooth solid wall

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Shiqi Zhou

Classical density functional theory is used to study the general aspects of wetting phenomena occurring in nonpolar neutral molecule system near a flat solid wall. Current cognitions of the wetting behavior are looked at, validated, corrected and extended. Several new observations are made: (i) the present theoretical calculations suggest that over a broad range of the surface potential parameters the pre-wetting transition temperature interval significantly reduces with the wetting temperature, and at the same time a continuous and monotonous increase of the wetting temperature is induced by decreasing the surface potential range and/or relative strength of surface atom versus fluid atom interaction. (ii) There exist lower limit values of both the surface potential range and the relative strength, below which the wetting transition is impossible. (iv) The present theoretical calculations confirm an experimentally found no adsorption occurring in weak surface potential substrates all the way to the relevant critical temperature by showing the impossibility of wetting at bulk critical temperature and its surroundings; moreover, the calculations extend the experimental observation to a wider parameter domain by indicating that the impossibility is not only unique feature of the weak surface potential substrates, but also applies to all situations of the surface potential range and relative strength. (v) With progressive increase of the relative strength and/or progressive decrease of the temperature, the interfacial phase behavior becomes increasingly complex: the (pre-)wetting transition and layering transition (which can be thermodynamically stable, metastable or even situated at supersaturated vapor phase) are intertwined closely; this challenges the popular knowledge that there is no (pre-)wetting for strong substrates for which the pre-wetting is replaced by the layering transitions.

Datum: 18.11.2017

Tolman’s length and limiting supersaturation of vapor

Publication date: Available online 13 November 2017
Source:Chemical Physics

Author(s): Nikolay V. Alekseechkin

The classical Kelvin formula for the equilibrium vapor pressure over a droplet of radius $R$ is extended to small radii and vapor non-ideality, from where the limiting supersaturation condition is obtained by relating the point $R = 0$ to the value of limiting (spinodal) supersaturation of vapor. The analysis of different dependences of the Tolman length on radius, $δ ( R )$, obeying this condition suggests that (i) the value of $δ ( 0 )$ is positive and the function $δ ( R )$ decreases with increasing radius; (ii) the curvature effect (the dependence of surface tension on radius) in the nucleation region is determined by the value of $δ ( 0 )$. At the same time, this effect is weakly sensitive to the form of the function $δ ( R )$ and insensitive to its asymptotic value $δ ∞$ .

Datum: 18.11.2017

Wavelength dependence of high-harmonic yield in stretched molecules

Publication date: 7 September 2017
Source:Chemical Physics, Volume 494

Author(s): Shengjun Yue, Hongchuan Du, Hongmei Wu, Jinbin Li, Bitao Hu

We study the wavelength dependence of harmonic yield in stretched molecules. It is found that when the laser field is perpendicular to the molecular axis, the harmonic yield has a slow scaling $λ - 4.27$ as the increase of the laser wavelength for the stretched molecule $H 2 +$ with the internuclear distance of 7a.u. compared with $λ - 5.11$ for $H 2 +$ at the equilibrium position. Further analysis shows that the narrower width of the initial wave-function in the momentum space is in charge of the slow wavelength scaling of the stretched molecule since it can make the wave-function spreading less during propagation. Moreover, a higher enhancement and a better wavelength scaling of harmonic yield both can be achieved at the optimal internuclear distance of 7a.u.

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Datum: 18.11.2017

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