Theoretical line lists of methane at T=80, 296, 500, 1000, 1500 and 2000K
All theoretical methane line lists included in TheoReTS are calculated by the variational method (except for "mixed abinitio/effective" model, see below # ))
from the following ab initio based potential energy surface (PES) and dipole moment surfaces (DMS):
A.Nikitin, M.Rey, and Vl.G.Tyuterev , Rotational and vibrational energy levels of methane calculated from a new potential energy surface, Chemical Physics Letters, 501, Issues 4-6, pp 179-186 (2011)
Ab initio DMS was defined in the same format as NRT DMS-2013 ( A.V. Nikitin, M. Rey, Vl.G. Tyuterev, New dipole moment surfaces of methane, Chem. Phys. Lett. , 565, 5–11 (2013)) but was recently improved using larger electronic basis set ( to be submitted)
Techniques of variational calculations are decribed in
Rey, M.; Nikitin, A. V., and Tyuterev, Vl. G. First-principles intensity calculations for the methane rovibrational spectra in the infrared up to 9300 cm-1. Phys. Chem. Chem. Phys., 15, 10049-10061 (2013)
Rey, M.; Nikitin, A. V., and Tyuterev, Vl. G. Predictions for methane spectra from potential energy and dipole moment surfaces: isotopic shifts and comparative study of 13CH4 and 12CH4. J.Mol.Spectroscopy, 291, 85-97 (2013).
M. Rey, A.V. Nikitin and Vl. G. Tyuterev, "Accurate first-principles calculations for CH3D infrared spectra from isotopic and symmetry transformations", J. Chem. Phys., 141 (2014) 044316
M. Rey, A.V. Nikitin, and Vl. G. Tyuterev , First predictions of rotationally resolved infrared spectra of Di-deuteromethane 12CH2D2 from potential energy and dipole moment surfaces, J.Phys . Chem. A, 119, 4763−4779 (2015)
M. Rey, A.V. Nikitin, and Vl. G. Tyuterev, Convergence of normal mode variational calculations of methane spectra: Theoretical linelist in the icosad range computed from potential energy and dipole moment surfaces, Journal of Quantitative Spectroscopy & Radiative Transfer 164 (2015) 207–220.
High-T line lists were calculated using the same approach as described in:
M. Rey, A.V. Nikitin and Vl. G. Tyuterev, "Theoretical hot methane line list up to 2000 K", Astrophysical Journal, 789 (2014) 1
but were further improved in TheoReTS using larger vibrational basis sets and higher reduction scheme.
Simulations of absorption/emission spectra and XS ( Spectra simulation section ) for high-T using full-suze data use the "Super-lines" compression technique
as discribed in
Rey, M.; Nikitin, A. V.; and Tyuterev, Vl. G, "TheoReTS - An information system for theoretical spectra based on variational predictions from molecular potential energy and dipole moment surfaces", J.Mol.Spectrosc., to be published (2016)
The partition Q(T) function was calculated as described in
Nikitin A.V., Krishna B.M., Rey M, Tashkun S.A., and Tyuterev VlG. Methane high- temperature partition function from contact transformations and variational calculations. J Quant Spectrosc Radiat Transfer 2015;167:53–63.
#) High-resolution line lists in the Dyad and Pentad randes of 12CH4 were obtained with "mixed abinitio/effective" model as described in
Vl.G. Tyuterev, S.A. Tashkun, M. Rey, R.V. Kochanov, A.V. Nikitin. , and T.Delahaye, Accurate spectroscopic models for methane polyads derived from a potential energy surface using high-order Contact Transformations. J. Phys. Chem. A.,117, 13779-13805 (2013)
using MOL_CT program suite. This new polyad model derived from the NRT PES permitted generating a spectral line lists for the Dyad and
Pentad bands with the accuracy 10-3 - 10-4 cm-1 for line positions combined with ab initio predictions for line intensities.