An Accurate, Extensive, and Practical Line List of Methane for the HITEMP Database
Robert J. Hargreaves, Iouli E. Gordon, Michael Rey, Andrei V. Nikitin, Vladimir G. Tyuterev, Roman V. Kochanov, Laurence S. Rothman
Abstract
Abstract A methane line list for the HITEMP spectroscopic database, covering 0–13,400 cm −1 (>746 nm), is presented. To create this compilation, ab initio line lists of 12 CH 4 from Rey et al. ApJ, 847, 105 (provided at separate temperatures in the TheoReTS information system), are now combined with HITRAN2016 methane data to produce a single line list suitable for high-temperature line-by-line calculations up to 2000 K. An effective-temperature interpolation model was created in order to represent continuum-like features over the temperature range of study. This model is advantageous to previously used approaches that employ so-called “super-lines,” which are suitable only at a given temperature and require separate line lists for different temperatures. The resultant HITEMP line list contains ∼32 million lines and is significantly more flexible than alternative line lists of methane, while accuracy required for astrophysical or combustion applications is retained. Comparisons against experimental observations of methane absorption at high temperatures have been used to demonstrate the accuracy of the new work. The line list includes both strong lines and quasi-continuum features and is provided in the common user-friendly HITRAN/HITEMP format, making it the most practical methane line list for radiative-transfer modeling at high-temperature conditions.