Lineshape and Moment Analysis in Isotropic and Anisotropic Interaction-Induced Light Scattering Spectra of Gaseous Helium

Abstract

Calibrated Raman spectra of the helium gas diatom at room temperature (294.5 K) have recently been measured over a wide range of intensities, with polarizations of the incident beam parallel and perpendicular to the direction of observation. From the resulting spectra, the isotropic and anisotropic components are separated for the helium diatom. For direct comparison with the measurements, quantum mechanical lineshapes are computed using recent model of the interatomic potential and models of the diatom polarizability tensor invariants as input. New empirical trace and anisotropy parameters, consistent with the spectroscopic measurements, are thus obtained for the helium gas. We compare these where possible with the existing computations based on classical physics, utilizing the first few even moments of the isotropic and anisotropic spectra. Good agreement with ab initio results in the literature is obtained and profiles calculated with these models are in excellent agreement with experiments.