The long tails at low and high frequency in the Rayleigh scattering by gases comprising tetrahedral molecules is attributed to rotational Raman scattering. The rotating part of the collision-induced polarizability is due to the dipole-quadrupole polarizability A and varies as the inverse fourth power of the separation of the two interacting molecules. The rotational section rules are ΔJ = 0, ±1, ±2, ±3, and quantitative agreement is obtained with the observed frequency dependence of the tail in methane. Contributions due to hyperpolarizability are found to be small. A value for the dipole-quadrupole polarizability A of methane is obtained by attributing the excess scattering over that implied by the dipole-induced-dipole model to A.
A. D. Buckingham and G. C. Tabisz, "Collision-induced rotational Raman scattering," Opt. Lett. 1, 220-222 (1977)