Interaction-induced light scattering by gaseous methane: the bound dimer contribution (CH4)2

The two-body depolarized, collision-induced light-scattering spectrum of gaseous methane has been measured and analyzed at five temperatures from 295 to 130 K. This spectrum consists of a low-frequency component, which is due to bound dimers (CH4)2, and an intermediate-frequency, purely translational contribution which is due to collisionally interacting CH4 pairs. (The high-frequency part, the rotational induced spectrum, was analyzed elsewhere and is of no great concern here.) The experimental spectra are compared with line-shape calculations based on a refined, empirical pair polarizability model and the spherical average of the Righini-Maki-Klein's potential [Chem. Phys. Lett. 80, 301 (1981)]. At all temperatures agreement of measured and computed profiles is observed on an absolute intensity scale.