Collision-induced Raman spectra of helium at 30 amagats are obtained, with incident beam polarization parallel and perpendicular to the direction of observation. The comparison reveals the presence of a polarized continuum not seen before in any gas. A wave-mechanical computation of this polarized spectrum, utilizing as input an ab initio calculation of the trace of the helium diatom polarizability, agrees with the observation. Thus a second, independent measurement of the isotropic part of the diatom polarizability is obtained.

• Received 13 March 1979

DOI:https://doi.org/10.1103/PhysRevLett.42.1473