INDUCED ROTATION-TRANSLATION SPECTRA OF SOLUTIONS OF $H_{2}$, HD, AND $D_{2}$ IN LIQUID ARGON.

This work was supported by a grant from the National Science Foundation. $^{1}$ H. Friedmann and S. Kimel, J. Chem. Phys., \emph{43}, 3925 (1965).Author Institution: Department of Chemistry Indiana UniversityDilute solutions of $H_{2}, D_{2}$, and HD in liquid argon are studied by examining the $1000-140 cm^{-1}$ region of their induced absorption spectra. For $H_{2}$ and $D_{2}$ several relatively sharp absorptions $(\Delta \nu{^{1}/_{2}}\approx 30 cm^{-1})$, which have a Lorentzian line shape and closely correspond to the expected transitions of the freely rotating solute molecules, are observed. The width of these lines appears to be due to uncertainty broadening which depends on the time the absorbing solute molecule spends in a particular solvent cavity. Other features, with a $150 cm^{-1}$ halfwidth, are believed to involve quantized translational energy levels of the solute. The HD spectrum is unusual in that the rotational selection rules are relaxed and transitions corresponding to $\Delta J = +2, +3$, and $+4$ are observed. Furthermore, all of the rotational absorption features are anomalously broad $(\Delta \nu^{1}/_{2}\approx50 cm^{-1})$ and their maxima are shifted from the gas-phase frequencies in an irregular pattern. Because of its asymmetrical mass distribution, rotational motion of HD is accompanied by a translation of the molecule in its solvent cavity. This rotation-translation interaction has been given quantitative form in a perturbation treatment by H. Friedmann and $S. Kimel,^{1}$ and the results are consistent with the observed selection rules, frequency shifts, and linewidths in the spectrum of HD in liquid argon