Interaction-induced translational Raman scattering of liquid argon: The spectral moments

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Abstract
The depolarized interaction-induced light scattering spectra of liquid argon have been measured, along the coexistence curve, at four different temperatures in the range 84.1–110.7 K. The experimental spectral moments have been evaluated, on an absolute scale, by means of a calibration procedure which makes use of a solution, in liquid argon, of about 1.4% hydrogen, whose rotational Raman lines are used as an intensity standard. The reproducibility of the calibration technique is very good and the present measurement fully confirms a previous experiment [D. Varshneya et al., Phys. Rev. A 23, 77 (1981)]. Molecular-dynamics computer simulation has been used to evaluate the first two even spectral moments in similar thermodynamic conditions. We used the pairwise additive potential of Barker, Fisher, and Watts and a model of the pair polarizability anisotropy which was derived from the low-density-gas collisional spectrum at room temperature. The overall agreement is good even if some refinements seem necessary. Since the effect of irreducible triple-dipole terms of both polarizability and potential is found to be smaller than the present experimental uncertainty, the small observed inconsistencies between measurement and computer simulation might be attributable to minor defects of the pair functions. More experimental data taken at different temperatures would help in refining the models.