Theoretical line lists of methaneSince November 2017, three types of data could be made available for downloading or simulations :
- Full line-by-line (LbL) linelists at low and/or room
reference temperatures without quantum identification of the transition (“full_LbL_lists”). The cut-off restrictions ( described case-by-case) permit to employ these “full_LbL_lists” within the temperatures range ( Tmin = 50 K , Tmax = 400 K), by an appropriate use of the T-dependence for intensities and for the partition functions.
- “Hybrid” compressed data sources designed for a fast spectra modeling.
At high temperatures, the spectra could be very congested including many millions or even billions of transitions ( see refs , ). To accelerate a modeling of spectral functions in these cases the initially computed full LbL lists are partitioned into two sets:
(b1) “Light lists” contain strong and medium transitions necessary for an accurate description of sharp features in absorption/emission spectra.
(b2) For a fast and efficient modeling of quasi-continuum cross sections, billions of tiny lines are compressed in “super-lines” libraries according to ref .
Warning (!) : For a correct use of these “hybrid” data sources, the spectral functions computed from (b1) “Light lists” and from (b2) “quasi-continuum” must be summed together. Otherwise , a part of the opacity would be missing.
- Linelists at various reference temperatures with full quantum identification of the transition (Assigned linelists) : currently few limited examples – under development.
References ( high-T and data compression methods):
- Rey, M., Nikitin, A.V., Tyuterev, V.G. “Theoretical hot methane line lists up to t = 2000 k for astrophysical applications”. Astrophysical Journal, 789 (1), art. no. 2, (2014); doi: 10.1088/0004-637X/789/1/2.
- Rey, M., Nikitin, A.V., Tyuterev, V.G. “Accurate Theoretical Methane Line Lists in the Infrared up to 3000 K and Quasi-continuum Absorption/Emission Modeling for Astrophysical Applications”. Astrophysical Journal, 847 (2), art. no. aa8909 (2017); doi: 10.3847/1538-4357/aa8909.
- M. Rey, A.V. Nikitin, Y. Babikov, V. Tyuterev, TheoReTS - An information system for theoretical spectra based on variational predictions from molecular potential energy and dipole moment surfaces // JMS, 2016, doi:10.1016/j.jms.2016.04.006.
Ab initio surfaces are described in refs:
- A.V. 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)
- A.V. Nikitin, M. Rey, and Vl.G. Tyuterev, "New dipole moment surfaces of methane", Chem. Phys. Lett. , 565, 5–11 (2013)
- A.V. Nikitin, M. Rey, and Vl.G. Tyuterev, "First fully ab initio potential energy surface of methane with a spectroscopic accuracy", J Chem Phys 145 (2016) 114309 http://dx.doi.org/10.1063/1.4961973
- A.V. Nikitin, M. Rey, and Vl.G. Tyuterev, "Accurate line intensities of methane from first-principles calculations", Journal of Quantitative Spectroscopy and Radiative Transfer, 200, pp. 90-99. (2017) DOI: 10.1016/j.jqsrt.2017.05.023