کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5427975 | 1508651 | 2015 | 14 صفحه PDF | دانلود رایگان |
- Detailed convergence study for the methane spectra (12CH4).
- Good agreement between the variational calculations and the WKLMC database.
- Variationally computed line lists (80Â K and 296Â K) for the icosad range 6280-7900Â cmâ1.
Accurate basis set convergence of first-principles predictions of rotationally resolved spectra at high energy range is a common challenging issue for variational methods. In this paper, a detailed convergence study for the methane spectra is presented both for vibrational and rotational degrees of freedom as well as for intensities. For this purpose, we use our previously reported nine-dimensional potential energy and dipole moment surfaces of the methane molecule [Nikitin et al. Chem Phys Lett 2011;501:179-86; 2013;565:5-11]. Vibration-rotation calculations were carried out using variational normal mode approach with a full account of the Td symmetry. The aim was to obtain accurate theoretical methane line lists for the wavenumber range beyond currently available spectra analyses. The focus of this paper is the complicated icosad range (6280-7900Â cmâ1) containing 20 bands and 134 sub-bands where over 90% of experimental lines still remain unassigned. We provide variational line lists converged to a “spectroscopic precision” for icosad transitions for T=80Â K and T=296Â K. The first one contains 70Â 300 lines and the second one 286Â 170 lines with the intensity cut-off 10â29cmâ1/(moleculecmâ2) with Jmax=18. An average error in line positions of theoretical predictions up to J=15 is estimated as 0.2-0.5Â cmâ1 from the comparisons with currently analyzed bands. Ab initio line strength calculations give the integrated intensity 4.37Ã10â20cmâ1/(moleculecmâ2) at T=80Â K for the sum of all icosad bands. This is to be compared to the integrated intensity 4.36Ã10â20cmâ1/(moleculecmâ2) of the experimental icosad line list recorded in Grenoble University [Campargue et al., J Mol Spectrosc 2013;291:16-22] using very sensitive laser techniques. The shapes of absorption bands are also in a good qualitative agreement with experimental spectra.
Journal: Journal of Quantitative Spectroscopy and Radiative Transfer - Volume 164, October 2015, Pages 207-220