RAYLEIGH-BRILLOUIN LIGHT-SCATTERING FROM NOBLE-GAS MIXTURES .2. PARTIAL STRUCTURE FACTORS

We derive a relation between the static structure factor for a mixture and experimental quantities that can be extracted from a Rayleigh-Brillouin light scattering experiment: the Landau-Placzek ratio and Brillouin shift. Partial structure factors are related to the thermodynamic quantities that characterize a mixture in a similar way as the Kirkwood-Buff integrals. In a He + Xe noble gas mixture, the spectrum is dominated by the contribution due to the Xe-Xe correlations in the mixture. We compare experimental results to calculations using the van der Waals equation of state. The other two partial structure factors can be obtained in an approximate way from a mixing rule for the partial static structure factors. Thus, it is possible to obtain approximate values for the isothermal compressibility, the osmotic compressibility, and the partial volume from a single experiment.