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

Rayleigh-Brillouin spectra of pure gases Xe, ${\mathrm{H}}_2$, ${\mathrm{D}}_2$ and gas mixtures Xe-He, ${\mathrm{H}}_2$-He, ${\mathrm{D}}_2$-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.