Collision-induced Raman spectra of neon and the diatom polarizability

Two collision-induced Raman spectra of gaseous neon are obtained, one with the linear polarization of the incident beam parallel to the direction of observation, and the other perpendicular. Absolute intensities are determined relative to nitrogen lines of known intensities. The comparison reveals the presence of a polarized contribution previously seen only in one other gas, helium. In addition, a depolarized component is obtained which agrees with and supplements an earlier measurement. For a direct comparison with experiment, collision-induced Raman spectra are also computed from wave mechanics, using models of the invariants (trace and anisotropy) of the neon diatom polarizability as input. For the depolarized spectrum an empirical model of the anisotropy is obtained which differs from the classical point-dipole expression by only 10% at the internuclear separation of 2.69 {}, the root of the interatomic potential. Similar attempts are made to develop an empirical trace model that is consistent with both the polarized spectrum and an earlier measurement of the second virial dielectric coefficient.