Overview of methane observed and theoretical spectra at T = 600 K for the entire range of present experimental records, 5400–8900 cm⁻¹: absorption cross section (XS in cm²/molecule) simulation with low resolution R = 2 cm⁻¹. Details for the three major absorbing intervals, 5400–6300 cm⁻¹ (“tetradecad” range), 6400–7700 cm⁻¹ (“icosad” range), and 8200–8900 cm⁻¹ (“triacontad” range), are given in the next sections.