Full-Dimensional Potential Energy and Dipole Moment Surfaces of GeH4 Molecule and Accurate First-Principle Rotationally Resolved Intensity Predictions in the Infrared

High resolution FTIR spectroscopy of germane: First study of 76GeH4 in the region of Tetrad of the strongly interacting ν1+ν2,ν1+ν4,ν2+ν3 and ν3+ν4 ro-vibrational bands

The infrared spectra of germane, purified and enriched up to 88.1% of ⁷⁶GeH₄, was measured at the temperature of (22.6±0.1) °C and different pressures with a Bruker Fourier transform infrared spectrometer IFS125HR and analyzed for the first time in the region of 2700-3200 cm^-1 where the stretching-bending Tetrad (ν₁+ν₂,ν₁+ν₄, ν₂+ν₃ and ν₃+ν₄ bands) of the ro-vibrational Octad of germane is located. The 3595 transitions belonging to the eight sub-bands of the Tetrad were assigned and theoretically analysed in the frame of the effective Hamiltonian model. The obtained set of 106 fitted parameters reproduces the initial 3595 experimental line positions with the d_rms=6.81×10^-4 cm^-1. The presence of numerous resonance interactions in the Tetrad is discussed.

On the method of precise abundance determination of isotopologues in a gas mixture

A method is presented which allows one to derive partial pressures of isotopologue molecules in a gaseous mixture under the conditions of rapid isotope exchange. For this purpose, isotopic relations between effective dipole moment parameters of a "parent" molecule and its related isotopically substituted species are derived on the basis of the general isotopic substitution theory. The efficiency of the method is illustrated. The result was derived for the fundamental bands and is valid for any asymmetric top molecule. The discussed general consideration offers the possibility to obtain analogous results both for any overtone as well as combinational bands of any asymmetric top molecule, and (with minor corrections) for any symmetric and/or spherical top molecule. The validity and efficiency of the general results are confirmed by comparison of the general results obtained in the present paper with the experimental results for the H2O/HDO molecules with a deviation of 3 to 4%.

Spin-Coupled Generalized Valence Bond Description of Group 14 Species: The Carbon, Silicon and Germanium Hydrides, XH n ( n = 1-4)

Although elements in the same group in the Periodic Table tend to behave similarly, the differences in the simplest Group 14 hydrides-XH _n (X = C, Si, Ge; n = 1-4)-are as pronounced as their similarities. Spin-coupled generalized valence bond (SCGVB) as well as coupled cluster [CCSD(T)] calculations are reported for all of the molecules in the CH _n/SiH _n/GeH _n series to gain insights into the factors underlying these differences. It is found that the relative weakness of the recoupled pair bonds of SiH and GeH gives rise to the observed differences in the ground state multiplicities, molecular structures, and bond energies of SiH _n and GeH _n. A number of factors that influence the strength of the recoupled pair bonds in CH, SiH, and GeH were examined. Two factors were identified as potential contributors to the decrease in the strengths of these bonds from CH to SiH and GeH: (i) a decrease in the overlap between the orbitals involved in the bond and (ii) an increase in Pauli repulsion between the electrons in the two lobe orbitals centered on the X atoms. Finally, an analysis of the hybridization of the SCGVB orbitals in XH₄ indicates that they are closer to sp hybrids than sp³ hybrids, which implies that the underlying cause of the tetrahedral structure of the XH₄ molecules is not a direct result of the hybridization of the X atom orbitals.

A variationally computed room temperature line list for AsH3

Calculations are reported on the rotation–vibration energy levels of the arsine molecule with associated transition intensities.

Understanding global infrared opacity and hot bands of greenhouse molecules with low vibrational modes from first-principles calculations: the case of CF4

Fluorine containing molecules have a particularly long atmospheric lifetime and their very big estimated global warming potentials are expected to rapidly increase in the future. This work is focused on the global theoretical prediction of infrared spectra of the tetrafluoromethane molecule that is considered as a potentially powerful greenhouse gas having the largest estimated lifetime of over 50 000 years in the atmosphere. The presence of relatively low vibrational frequencies makes the Boltzmann population of the excited levels important. Consequently, the "hot bands" corresponding to transitions among excited rovibrational states contribute significantly to the CF4 opacity in the infrared even at room temperature conditions but the existing laboratory data analyses are not sufficiently complete. In this work, we construct the first accurate and complete ab initio based line lists for CF4 in the range 0-4000 cm-1, containing rovibrational bands that are the most active in absorption. An efficient basis set compression method was applied to predict more than 700 new bands and subbands via variational nuclear motion calculations. We show that already at room temperature a quasi-continuum of overlapping weak lines appears in the CF4 infrared spectra due to the increasing density of bands and transitions. In order to converge the infrared opacity at room temperature, it was necessary to include a high rotational quantum number up to J = 80 resulting in 2 billion rovibrational transitions. In order to make the cross-section simulation faster, we have partitioned our data into two parts: (a) strong & medium line lists with lower energy levels for calculation of selective absorption features that can be used at various temperatures and (b) compressed "super-line" libraries of very weak transitions contributing to the quasi-continuum modelling. Comparisons with raw previously unassigned experimental spectra showed a very good accuracy for integrated absorbance in the entire range of the reported spectra predictions. The data obtained in this work will be made available through the TheoReTS information system (http://theorets.univ-reims.fr, http://theorets.tsu.ru) that contains ab initio born line lists and provides a user-friendly graphical interface for a fast simulation of the CF4 absorption cross-sections and radiance under various temperature conditions from 80 K to 400 K.