Molecular Physics

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ISSN / EISSN : 0026-8976 / 1362-3028
Published by: Informa UK Limited (10.1080)
Total articles ≅ 18,935
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Tim Stauch, Brad Ganoe, Jonathan Wong, JoonHo Lee, Adam Rettig, Jiashu Liang, Jie Li, Evgeny Epifanovsky, Teresa Head-Gordon,
Published: 14 October 2021
Abstract:
Magnetic properties of molecules such as magnetisabilities represent second-order derivatives of the energy with respect to external perturbations. To avoid the need for analytic second derivatives and thereby permit evaluation of the performance of methods where they are not available, a new implementation of quantum chemistry calculations in finite applied magnetic fields is reported. This implementation is employed for a collection of small molecules with the aug-cc-pVTZ basis set to assess orbital optimised (OO) MP2 and a recently proposed regularised variant of OOMP2, called κ-OOMP2. κ-OOMP2 performs significantly better than conventional second-order Møller–Plesset (MP2) theory, by reducing MP2's exaggeration of electron correlation effects. As a chemical application, we revisit an old aromaticity criterion called magnetisability exaltation. In lieu of empirical tables or increment systems to generate references, we instead use straight chain molecules with the same formal bond structure as the target cyclic planar conjugated molecules. This procedure is found to be useful for qualitative analysis, yielding exaltations that are typically negative for aromatic species and positive for antiaromatic molecules. One interesting species, N2S2, shows a positive exaltation despite having aromatic characteristics. GRAPHICAL ABSTRACT
Swetha Sara Sabu, S. Jane Anto Simplica, ,
Published: 14 October 2021
Abstract:
The hardness of an atom is an important atomic parameter. The present work offers an ansatz to compute absolute hardness (η) based on the conjoint action of three periodic properties, namely effective nuclear charge, electronegativity and radii of atoms of 103 elements of the periodic table. The present computation involves a statistical regression analysis. The new hardness values follow all the sine qua non of periodic property and include relativistic effects. Our computed data runs hand in hand with some popular existing hardness scale. Also, Hardness Equalization Principle is satisfactorily established through our computed molecular hardness. GRAPHICAL ABSTRACT
Gai Shi, , Pengzhen Tian, Zhijun Li
Published: 13 October 2021
Abstract:
An direct kinetics study of the (CH2OH)2 + O(3P) and (CH2OH)2 + H reactions was performed over the temperature range of 300–1500 K. The geometries of all stationary points were optimised at the M06-2X/cc-pVQZ level of theory. The electronic energies were refined by CCSD(T)/CBS and QCISD(T)/cc-pVTZ methods. The rate coefficients were calculated using canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) correction. The results showed that the channels of hydrogen abstraction from the CH2 group were most kinetically favourable at the temperature less than 1300 K and have positive temperature dependence. The OH-transfer channels were ignorable. GRAPHICAL ABSTRACT
S. Tahereh Alavi, Graham A. Cooper,
Published: 13 October 2021
Abstract:
Coupling covariance map analysis with ultrafast laser-induced Coulomb explosion imaging (CEI) enabled us to characterise the dissociative ionisation dynamics of methoxycarbonylsulfenyl chloride (H3COCOSCl). We applied a 3D multi-coincidence detection technique which is necessary for covariance imaging analysis. With the aid of such analysis, we found meaningful correlations between several product ion pairs that revealed different fragmentation channels. A weak, narrow correlation in the covariance image of H3COC(O)+/Cl+ was assigned to a concerted three-body dissociation channel. We also observed a broadly distributed correlation in the covariance image of COS+/HCO+, which is ascribed to a multi-body fragmentation channel. Ab initio calculations were carried out to determine the likely starting structures. A very sharp feature in the covariance image of Cl+/ CH3+ indicated that this pair of ions is produced from a two-body-like fragmentation event of CH3Cl2+. We show by direct comparison with CEI of CH3Cl that, contrary to a previously suggested assignment, this ion pair is produced from CH3Cl, which is formed either in the bubbler or gas line before the molecular beam interacts with the laser beam. GRAPHICAL ABSTRACT
, L. Manceron, R. Armante, F. Kwabia-Tchana, P. Roy, D. Doizi
Published: 13 October 2021
Abstract:
This paper is the first of two back-to-back works, whose goal is to update the existing line positions and intensities spectroscopic parameters for the 5.8 µm region of nitric acid in the HITRAN or GEISA spectroscopic databases. This first study is devoted to the generation of first linelists for the ν2+ν9-ν9, ν2+ν7-ν7 and ν2+ν6-ν6 hot bands in the 5.8 µm region, whereas the second study will concern the positions and intensities for the ν2 band centred at 1709.567 cm−1. High-resolution Fourier transform spectra were recorded in the 5.8 µm and in the 4.2–4.6 µm spectral ranges. The identification of the ν2+ν9, ν2+ν7 and ν2+ν6 bands of HNO3 at 2165.0036, 2285.9657 and 2351.216 cm−1, respectively, was performed, and several assignments were confirmed by searching for ν2+ν9-ν9 and ν2+ν7-ν7 transitions within those of ν2 at 5.8 µm. Both ν2+ν6 and ν2+ν9 bands are highly perturbed. Surprisingly, both ν2+ν9 and ν2+ν9-ν9 bands exhibit large amplitude torsional splittings of ∼0.043 cm−1. This is presumed to be due to the existence of an anharmonic resonance that couples together the 2191 energy levels with those of a dark state involving high excitation in the ν9 large amplitude OH torsional mode. GRAPHICAL ABSTRACT
, A. M. Solodov, V. M. Deichuli, V. I. Starikov
Published: 13 October 2021
Abstract:
The water vapour line broadening (γ) and shift (δ) coefficients for 319 lines of 11 vibrational bands 2ν3, 2ν2 +ν3, 3ν2+ν3, 5ν2, 6ν2, ν1+ν3, ν1+ν2+ν3, ν1+2ν2, ν1+3ν2, 2ν1, and 2ν1+ν2 from the spectral region 7520–8586 cm–1 induced by air pressure were measured with a Bruker IFS 125 spectrometer. The measurements were performed at a spectral resolution of 0.01 cm–1 and over a wide air pressure range. The calculations of the line-shift coefficients δ were performed in the framework of a semi-classical method. The measured air-broadening coefficients γ were combined with literature data for air- and N2-broadening coefficients γ measured for the lines in the 380–22,593 cm–1 spectral region. Combined experimental data for N = 4110 measured coefficients γ of 76 vibrational bands of H2O molecules were fitted to the empirical functions. The computed coefficients γ derived from the fitted parameters were statistically compared with the measurements. The vibrational dependence of the measured γ values and their compatibility is discussed. GRAPHICAL ABSTRACT
Enrique Díaz-Herrera, Eduardo Cerón-García, Anthony Bryan Gutiérrez,
Published: 13 October 2021
Abstract:
Fluids interacting with Lennard-Jones and Square Well potentials reach thermodynamic equilibrium forming two coexisting phases when simulated within the liquid–vapour spinodal region. If molecular dynamics simulations in the NVT ensemble are performed on a fluid kept in a cubic cell with periodic boundary conditions, liquid and vapour phases at equilibrium are separated by a process of spinodal decomposition. In the vapour side of the spinodal curve, spherical, cylindrical, and slab type liquid structures are formed, depending on the total density. Under the mentioned conditions, in the liquid side of the spinodal, vapour bubbles with the same shapes, surrounded by liquid, are formed. Results from this work suggest that as the simulation system size increases, the spinodal curve approaches the orthobaric, but it converges to a position closer to the coexistence curve but separated from it. The same thing happens for both potential models simulated. This is in sharp contrast with previous findings by Errington, McDowell, Binder and coworkers, where they conclude that ‘Only for infinitely large systems does the effective spinodal density converge to the macroscopic coexistence vapor density.’ GRAPHICAL ABSTRACT
E. S. Reedy, J. Rademacher, R. Szabla,
Published: 13 October 2021
Abstract:
The 2Πg←X2Σu+ electronic spectrum of C5+ in the gas-phase with origin band at 513nm is reported following experiments in a cryogenic ion trapping instrument. Buffer gas-cooled C5+ ions, generated by laser vaporisation of graphite, were investigated using two action spectroscopy approaches. Laser-induced dissociation of weakly bound C5+−Hen complexes synthesised in the trap reveal a linear dependence of the absorption energies on n allowing prediction of those of the bare ion C5+. These results are confirmed in two colour experiments on C5+, by monitoring fragmentation into the C3++C2 product channel. The data are supplemented with high-level electronic structure calculations which support the assignment of D∞h symmetry to the ground electronic state. These laboratory results provide the requisite data needed for spectroscopic detection of this structure in terrestrial and extraterrestrial environments. GRAPHICAL ABSTRACT
Lucas E. Aebersold, ,
Published: 11 October 2021
Abstract:
The Born–Oppenheimer approximation is the fundamental approximation in the quantum-mechanical description of molecules, and holds true in most applications for ground-state properties and to a lesser extent for excited states. In situations where the coupling of electronic and nuclear motion becomes significant, for example, in strong-field induced time-dependent processes, the electron-nuclear interaction must be described beyond the Born–Oppenheimer picture. Presented here are multiconfiguration electron-nuclear dynamics simulations with and without a laser pulse excitation for the diatomic molecules H2, HeH+, LiH, BeH+, Li2, and N2, taking into account electron-nuclear coupling. The computational approach allows a direct propagation of the electron-nuclear wave function, thus avoiding the construction of potential energy surfaces. With this approach, ground-state and time-dependent properties, including equilibrium bond lengths, dipole moments, and electronic, vibrational, and high-harmonic spectra are obtained. For some of the diatomics, manifestations of nonadiabatic effects are observed in the high-harmonic spectra, where both an uptake of nuclear motion and electronic excitation into higher-lying excited states can occur, resulting in an effective driving force that displaces the nuclei from the equilibrium position. Isotope effects can also be observed in electronic excitation spectra. GRAPHICAL ABSTRACT
, Akira Satoh
Published: 11 October 2021
Abstract:
We have developed a Brownian dynamics simulation technique for a cubic magnetic particle suspension in a simple shear flow in order to elucidate the relationship between the particle aggregates and the magnetorheological characteristics. A magnetic field is applied in the direction normal to the shearing plane. In a weak applied magnetic field, if the magnetic particle–particle interaction strength is sufficiently large, the particles aggregate to form closely-packed clusters even when subject to the influence of the shear flow. As the magnetic field strength is increased, the closely-packed aggregate structures are transformed into chain-like structures. The net viscosity is increased because the chain-like clusters give rise to a larger resistance to the flow field. As the magnetic field strength is further increased, the chain-like clusters grow into wall-like clusters aligned in the direction of the magnetic field. If the wall-like clusters are the predominant clusters, a magnetic force arises due to a characteristic of the particle arrangement in the wall-like clusters that tends to accelerate the flow field and, as a consequence, decrease the net viscosity. From these results, it may be suggested that under certain conditions a magnetic cubic particle suspension may exhibit a negative contribution to the magnetorheological characteristic. Highlights of the present study GRAPHICAL ABSTRACT
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