Comment on 'Brillouin scattering studies of liquid argon at hightemperatures and high pressures' [J. Chem. Phys. 129, 154503 (2008)]

摘要

In Ref. 1, the authors report on Brillouin scattering mea-surements on argon at high pressure (P) and temperature (T)conditions from which they obtain experimental data for thesound velocity and refractive index of the fluid phase alongseveral isotherms up to 503 K and respective melting pres-sures. Starting from the refractive index data, they derive thedensity of fluid argon along the studied isotherms using theLorentz-Lorenz relation, under the assumption that the elec-tronic polarizability of argon does not vary with P-T condi-tions. Applying the same reasoning to the data obtained atthe solid-fluid coexistence, they obtain values for the densityof the fluid and solid phases at coexistence, from which theyderive the volume jump ΔV_mat melting (or volume).This results in a highly unusual observation, that is, the in-crease in ΔV_mwith temperature along the melting line. Inthis comment I show that this finding is neither supported byavailable experimental data nor theoretical calculations, andthat this is due to an erroneous determination of the fluiddensities.