On a pair-potential-independent criterion for D.I.D. Light Scattering

It is shown that, for a gas of isotropic molecules, the dipole-induced-dipole (D.I.D.) mechanism in the first approximation (multiple scattering limited to double scattering) is the only one which implies a limit value of 2 at low densities for the ratio of the Raman and Rayleigh depolarization factors in the collision induced scattering. This is a necessary and sufficient, pair-potential- independent criterion for the pure D.I.D. model, to be used in experimental investigations.