Showing papers by "Vl.G. Tyuterev published in 2017"
TL;DR: In this article, an accurate rovibrational analysis of the upper part of the Tetradecad 12 CH 4 spectrum in the 5855-6250 cm −1 region is reported.
Abstract: Accurate rovibrational analysis of the upper part of the Tetradecad 12 CH 4 spectrum in the 5855–6250 cm −1 region is reported for J ≤ 10 The analysis uses the WKLMC experimental line list previously obtained in Grenoble by Cavity Ring Down Spectroscopy and Differential laser Absorption Spectroscopy at T = 296 K Based on a previously published ab initio potential energy surface, the full Hamiltonian of methane nuclear motion was reduced to an effective Hamiltonian using high-order Contact Transformation method with a subsequent empirical optimization of parameters Overall, more than 3200 12 CH 4 transitions are assigned adding about 1800 new assignments to those provided in the HITRAN database for 12 CH 4 in the region The 12 CH 4 experimental line positions were fitted with RMS standard deviations of 00015 cm −1 and 2381 line intensities were modeled using an effective dipole moment with the RMS deviation of 8% Rovibrational energy levels of sixteen vibrational states of the upper part of the Tetradecad system were determined For the first time all three sub-levels of the weak 4ν 2 band were assigned As a result, a new version of the WKLMC list for natural methane at 296 K is provided including the new assignments in the 5855–6250 cm −1 region
29 citations
TL;DR: In this paper, a line-shape study was carried out to obtain the CH 4 −CH 4 and CH 4 air half-width coefficients, CH 4 -CH 4 shift coefficients and off-diagonal relaxation matrix element coefficients for methane transitions in the spectral range known as the methane octad.
Abstract: Due to the importance of methane as a trace atmospheric gas and a greenhouse gas, we have carried out a precise line-shape study to obtain the CH 4 –CH 4 and CH 4 –air half-width coefficients, CH 4 –CH 4 and CH 4 –air shift coefficients and off-diagonal relaxation matrix element coefficients for methane transitions in the spectral range known as the “ methane Octad ”. In addition, the associated temperature dependences of these coefficients have been measured in the 4300–4500 cm −1 region of the Octad. The high signal to noise ratio spectra of pure methane and of dilute mixtures of methane in dry air with high resolution have been recorded at temperatures from 148 K to room temperature using the Bruker IFS 125 HR Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory, Pasadena, California. The analysis of spectra was done using a multispectrum non-linear least-squares curve fitting technique. Theoretical calculations have been performed and the results are compared with the previously published line positions, intensities and with the line parameters available in the GEISA and HITRAN2012 databases.
20 citations
TL;DR: In this article, an ab initio potential energy surface was reduced to an effective Hamiltonian using high-order Contact Transformations method adapted to polyads of symmetric top AB 3 -type molecules with subsequent empirical optimization of parameters.
Abstract: Improved analysis of positions and intensities of phosphine spectral lines in the Octad region 2733–3660 cm −1 is reported. Some 5768 positions and 1752 intensities were modelled with RMS deviations of 0.00185 cm −1 and 10.9%, respectively. Based on an ab initio potential energy surface, the full Hamiltonian of phosphine nuclear motion was reduced to an effective Hamiltonian using high-order Contact Transformations method adapted to polyads of symmetric top AB 3 -type molecules with a subsequent empirical optimization of parameters. More than 2000 new ro-vibrational lines were assigned that include transitions for all 13 vibrational Octad sublevels. This new fitting of measured positions and intensities considerably improved the accuracy of line parameters in the calculated database. A comparison of our results with experimental spectra of PNNL showed that the new set of line parameters from this work permits better simulation of observed cross-sections than the HITRAN2012 linelist. In the 2733–3660 cm −1 range, our integrated intensities show a good consistency with recent ab initio variational calculations.
13 citations