Collision–induced absorption in gaseous methane at low temperatures

Abstract

A recently developed theory for collision-induced absorption in methane is compared with experimental results over a wider spectral range and at lower temperatures than previously reported. The present experimental results covering the frequency range below 400 cm −1 exhibit good agreement with other recently published data. The theory shows excellent agreement with experiment in the low-frequency region below approximately 200 cm −1 but underestimates the experimental data somewhat at higher frequencies. Possible theoretical reasons for this discrepancy are given. The theory represents a simple method of obtaining a good estimate of the collision-induced absorption spectra of methane in this frequency region and for extrapolating to lower temperatures for which experimentation is not feasible. In addition, the moments α 1 and γ 1 are compared with earlier determinations and indicate good agreement with the previously obtained values for the octupole and hexadecapole moments of methane.