Low temperature CILS study in gaseous helium over a large spectral domain

Abstract

For the first time, binary Collision-Induced Light Scattering (CILS) spectral intensities have been measured in gaseous helium at a low temperature (99.6 K). The depolarized spectrum and the depolarization ratio have been extracted in the frequency range 5–225 cm−1. The isotropic spectrum has been obtained in the spectral domain 100–225 cm−1. The spectral intensities have been calibrated on an absolute scale (cm6) by means of rotational lines of H2 and D2. We have compared our experimental results with theoretical spectra computed quantum-mechanically. Several incremental polarizability models have been checked, putting the emphasis on the most up-to-date ab initio ones which are available in the literature. This study, combined with the one made at room temperature, enables one to definitely decide on the quality of the induced polarizability models and therefore to acquire a deeper understanding of the atomic collision dynamics at short internuclear separations.