Raman studies of the orientational motions of small diatomics dissolved in argon

Abstract

We report a study of the orientational motions of oxygen and nitrogen dissolved in argon, using Raman spectroscopy. First, second, and fourth moments are reported for the rotation and vibration–rotation bands of these molecules at various concentrations along the liquid–vapor coexistence curve. It was found that less mean square torque is exerted on an oxygen molecule in argon solution than in the pure liquid at similar temperatures. The nitrogen data are probably in accord with this, although the experimental uncertainty is greater. Experimental values of the second moments are significantly in excess of the predicted classical values, even including important quantum corrections. This is probably due to ’’collision-induced’’ effects which were not accounted for in the moment analysis. Molecular dynamics simulations of rigid rotor ’’nitrogen’’ were made and the first order DID contributions to the collision-induced vibration–rotation spectrum were calculated. Even leaving out any high frequency overlap mechanism, the effect on the second moment was suprisingly large.