Collision-induced light scattering by fluids of optically isotropic molecules: Comparison of results of two model studies

We report results of theoretical and computer-simulation studies of collision-induced light-scattering (CILS) intensities in fluids of optically isotropic molecules. Depolarized Rayleigh scattering in monatomic and spherical-top polyatomic fluids and depolarized Raman scattering at the completely symmetric vibrational mode of spherical-top molecular fluids are considered. Lennard-Jones potential is used to model intermolecular interactions. The collective polarizability is described by the first-order dipole--induced-dipole (DID) interaction model. CILS intensities for this model are evaluated by molecular-dynamics (MD) simulation at two temperatures and a set of densities. These results and those of earlier MD simulations are compared to the lattice-gas approximation to the same model. Results for the lattice-gas model (LGM) are obtained by Monte Carlo simulation on a face-centered-cubic lattice with Lennard-Jones and DID interactions between occupied nearest-neighbor sites. We find that the MD results for CILS intensities are weakly temperature dependent and that they agree well with the high-temperature version of the LGM. We also find that the LGM predicts a strong temperature dependence of these quantities, in disagreement with the MD results. Reasons for the inaccuracy of the LGM predictions and possible improvements of this model are discussed.