Higher order interaction-induced effects on Rayleigh light scattering by molecular liquids

Abstract

Molecular dynamics (MD) computer simulation was used to study Rayleigh light scattering (LS) in oxygen and carbon disulfide liquids. Results are presented for one thermodynamic state of oxygen (82 K, 1.215 g/cm3) and two thermodynamic states of CS2 (193K, 1.42 g/cm3 and 293 K, 1.30 g/cm3). The molecular trajectories were generated using Lennard-Jones atom–atom potential models. LS spectra were calculated using the dipole–induced dipole (DID) model for the interaction-induced polarizability. The results obtained for the LS intensities, time correlations, and line shapes, using the first-order perturbation theory for the system polarizability, based on this model, are compared to the exact DID model results. We find that the relative contribution of the higher order DID terms to LS spectra of these liquids can be correlated with the magnitudes of the isolated molecule isotropic and anisotropic polarizabilities. As a result of this, these terms have a very small effect on O2 LS spectra, but that they make a large contribution to CS2 spectra. In CS2, the main consequence of including these terms is to substantially increase the orientational component and decrease the collision-induced component of the depolarized Rayleigh spectrum. Higher order DID interaction terms also lead to a faster initial relaxation of the collision-induced components of isotropic and depolarized spectra. The MD effective polarizability and depolarized LS line shape data for CS2 at 293 K are compared with experimental results. We find that the exact DID model results are in much better agreement with experiment than those obtained using the first-order DID model.