INFRARED ABSORPTION OF HD IN LIQUID ARGON.

Abstract

The induced infrared spectrum of a solution of HD in liquid argon $(87^{\circ}K)$ has been observed. HD rotates in this system, and its spectrum is qualitatively similar to the induced spectrum of $H_{2}$ or $D_{2}$ in liquid argon. While the relatively sharp features in the spectrum correspond to vibration-rotation transitions calculated for gas phase HD, the broader absorptions are assigned to vibration-translation combination bands. The induced spectrum of HD is unusual in that vibration-rotation features corresponding to $\Delta J = 0, \pm 1, +2, +3$, and $+4$ are observed. It has also been observed that the frequencies of transitions involving the $J = 1$ rotational level are shifted approximately $20 cm^{-1}$ from their corresponding gas phase frequencies, although other rotational features are shifted less than $10 cm^{-1}$. These effects can be explained in terms of a simple model involving rotation-translation coupling, which occurs because the center of mass and the center of interaction of an HD molecule are slightly separated.