Collision induced light scattering from fluids composed of tetrahedral molecules

The two body depolarized collision-induced light scattering spectrum of 2, 2-dimethyl prpane (neopentane) in the vapour state is presented. The polarization ratio is given as well. The point dipole-induced-dipole (DID) effect is shown to account for 94 per cent of the total intensity in contrast to previous studies. At low frequencies the line shape is dominated by bound dimers, whereas the intermediate frequency range up to 60 cm-1 is well described by a DID free trajectory binary collision model. The high frequency wings are discussed in terms of the collision-induced rotational Raman (CIRR) effect and estimates for the dipole-quadrupole and dipole-octopole polarizabilities A and E, respectively, are obtained. It is demonstrated that the hierarchy of effects constituting the CIRR-model converges slowly for large frequencies and that the inclusion of a delicate balance between negative overlap corrections and positive corrections to the truncated DID-anisotropy is necessary for a quantitative description at very large |v|.