Third virial coefficients of collision-induced, depolarized light scattering of hydrogen.

Abstract

A combined experimental and theoretical-computational study of three-body effects in collision-induced, depolarized light scattering in compressed hydrogen gas is reported. It includes measurements of the translational Raman line profile at a temperature of 50 K and gas densities from 20 to 530 amagats that are analyzed in terms of density-squared and -cubed components. The third virial coefficients of the zeroth, first, and second spectral moments are determined. The study also includes semiclassical calculations of the third virial coefficients of the zeroth and first spectral moments that are based on refined, empirical pair-polarizability models. Quantum corrections of the Wigner-Kirkwood type are significant. A comparison of measurement and theory suggests that at 50 K a positive irreducible component affects the measurement; its magnitude amounts to roughly 40% of the pairwise-additive component. Theoretical estimates of the long-range (classical) irreducible anisotropy of the polarizability of three-body complexes suggest a positive spectral contribution that, however, amounts to just a fraction (namely, about 1/4) of the difference observed between measurement and theory. At 297 K such measurements also exist and suggest a negative irreducible component that is probably nonclassical, of an overlap (short-range) nature.