ExoMol line lists – IV. The rotation–vibration spectrum of methane up to 1500 K

Abstract

A new hot line list is calculated for 12 CH 4 in its ground electronic state. This line list, called 10to10, contains 9.8 billion transitions and should be complete for temperatures up to 1500 K. It covers the wavelengths longer than 1 m and includes all transitions to upper states with energies below hc 18 000 cm -1 and rotational excitation up to J = 39. The line list is computed using the eigenvalues and eigenfunctions of CH 4 obtained by variational solution of the Schrdinger equation for the rotation-vibration motion of nuclei employing program TROVE and a new 'spectroscopic' potential energy surface (PES) obtained by refining an ab initio PES (CCSD(T)-F12c/aug-cc-pVQZ) through least-squares fitting to the experimentally derived energies with J = 0-4 and a previously reported ab initio dipole moment surface (CCSD(T)-F12c/aug-cc-pVTZ). Detailed comparisons with other available sources of methane transitions including HITRAN, experimental compilations and other theoretical line lists show that these sources lack transitions both higher temperatures and near-infrared wavelengths. The 10to10 line list is suitable for modelling atmospheres of cool stars and exoplanets. It is available from the CDS data base as well as at www.exomol.com.