Improved line list of methane in the 900–1050 cm-1 region

Abstract

Four spectra of methane in natural isotopic abundance in the 900–1050 cm^-1 region were recorded using a Fourier transform spectrometer in Tomsk, Russia, with long optical paths 167 m and 1058 m at temperatures 28 and 51 °C. Line positions and intensities were retrieved by non-linear least-squares curve-fitting procedures and analyzed using effective Hamiltonian and effective dipole moment models. The enhanced absorption at long paths permitted to measure new transitions: in cold bands up to J_max = 28 and in hot bands up to J_max = 20. The new experimental line list contains line positions and intensities for 2570 features. Quantum assignments were made for 1246 lines of the main isotopologue ¹²CH₄. Comparisons of the theoretical absorption simulations with experimental spectra revealed a considerable improvement compared to the HITRAN2020 database. All assigned 1246 line positions were fitted to RMS standard deviations of 0.00065 cm^-1.