Far-Infrared Spectra of HCl and HBr in Solid Solutions

Abstract

The far‐infrared absorption spectra of HCl, DCl, HBr, and DBr in solid solutions in the hosts Ar, Kr, Xe are described in the wavelength range 33–100 cm⁻¹. One band was observed for each solid solution close to the presumed phonon band of the respective host. The absorption peak frequency was identical for HCl and HBr for all three hosts investigated. The observed spectra are discussed in terms of both a localized mode model and activated phonon bands, the latter affording the more likely interpretation. The principal source of the observed intensity is demonstrated to be the coupling between rotation of the solute molecule in the host lattice and translational motion.