Light-scattering studies of moderately dense gases. II. Nonhydrodynamic regime

Rayleigh-Brillouin spectra of pure gases Xe, H₂, D₂ and gas mixtures Xe-He, H₂-He, D₂-He have been measured at room temperature and over a range of pressures, and the results compared with hydrodynamic and kinetic-theory calculations. It is shown that in the concentration range studied, nonideality and thermal-diffusion effects are both small in the hydrogen-helium mixtures, whereas these effects are significant in the Xe-He mixtures. The existing kinetic-model description based on the Boltzmann equation for Maxwell molecules needs to be modified in order to account for the Xe-He data.