Infrared Spectra of Highly Compressed Gas Mixtures of the Type HCl+X. A Theoretical Study

Publisher Website
Google Scholar
Abstract
A theory is proposed to explain the ir spectra of highly compressed gas mixtures of the type HCl+X (or HBr, HF with X=He, Ar, Xe, N2, CO, etc.). This theory is based on the following three hypotheses: (1) The compressed mixture is formed of three molecular species, free HCl (or HBr, HF, etc.), free X, and bound van der Waals molecules (HCl···X). (2) In thermodynamic equilibrium, the system is subject to the law of mass action: HCl+X⇌(HCl···X). (3) The equilibrium constant is given by the standard formula K(T) = exp(—ΔF/RT). Using these hypotheses, the spectral perturbations are explained in terms of the calculated properties of the bound van der Waals molecules. The theory predicts that three limiting types of van der Waals molecules exist according to whether the energy of coupling between the rotation of HCl and the over‐all rotation of the complex is (1) smaller than the energy of the over‐all rotation of the complex [Coupling Case (1)], (2) larger than the energy of the over‐all rotation of the complex but smaller than the energy of the rotation of HCl [Coupling Case (b)], (3) much larger than the energy of rotation of HCl [Coupling Case (c)]. The energy expressions are given for the three coupling cases, the equilibrium constants K (T) are calculated and the spectral perturbations are analyzed. In particular, the fine structure of the induced band is discussed.