Depolarized light scattering and neutron scattering spectra for noble gas fluids

Using the technique of interaction-induced depolarized light scattering (DILS) the four-point dynamic correlation function is probed. Here, we discuss three different decoupling approximations which express the four-point dynamic correlation function in terms of two-point dynamic (Van Hove) correlation functions. We show that the experimental results of the integrated DILS intensity of Ar as a function of density can be reproduced satisfactorily by one of the decoupling approximations for densities up to the critical density. The line shape of the DILS spectrum of Xe in the liquid phase is compared with the decoupling approximation using the two-point dynamics correlation function obtained from neutron scattering experiments on Ar at the corresponding state. It is shown that the low-frequency part of the model calculation is consistent with the experimental DILS results. In this frequency range, in the liquid phase, the DILS spectrum appears to be mainly determined by density fluctuations with wavelengths of the order of the diameter of the particles. The influence of different expressions for the pair polarizability on the model calculations is discussed.