Far infrared spectra of van der Waals molecules in HCl–noble gas mixtures

Abstract

Results of far infrared measurements on HCl–noble gas mixtures in the region 14–240 cm−1 at low temperatures and densities between 0.4 and 4 amagat, are presented. Between the free HCl rotational lines distinct absorption features are observed that are assigned to X–HCl van der Waals molecules (X=HCl, Ar, Kr, Xe). Various internal motions of the complexes are considered and it is concluded that the spectra originate from internal rotatory motion of the HCl subunit. A model for an effective angular potential governing this motion is discussed. The trends in the experimental spectra suggest that the well depth increases in the series Ar–Kr–Xe, reflecting an increase in anisotropy in the above order.