Pressure-induced widths and shifts for the ν3 band of methane

Abstract

Widths and shifts of methane lines perturbed by nitrogen are calculated using a complex-valued implementation of Robert–Bonamy (RB) theory. The static intermolecular potential is described as a sum of electrostatic forces and Lennard-Jones (6-12) atom–atom terms, using literature values for all physical parameters. Vibrational dependence of the isotropic potential is obtained from the polarizability of methane assuming a dispersion interaction. The repulsive part of the Lennard-Jones accounts for the greatest part of widths, while dispersion interactions are largely responsible for shifts. Although the average error between calculated and observed linewidths (up to J=8) is less than 6%, their distribution suggests the influence of interactions not described in the present theory.