Non-Markovian far-infrared spectra of a diatomic molecule in rare-gas liquids.

Abstract

The far-infrared spectra of diatomic polar molecules, immersed in a rare-gas liquid, are calculated using two non-Markovian formalisms: the total-time-ordering-cumulant (TTOC) and the partial-time-ordering-cumulant (PTOC) formalisms. Both TTOC and PTOC spectra coincide in the Markovian limit. The interaction between the diatomic molecule and the liquid is described by means of a directing intermolecular field with known statistical properties. In the secular approximation both TTOC and PTOC spectra contain a sum of resonances which become Lorentzian in the Markovian limit. The interference effect among resonances is taken into account using iterative methods in which the secular profile is the first term in the iterative process. We apply the theory to calculate the far-infrared spectra (0\char21{}200 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) of a HCl molecule in Ar, Kr, and Xe liquids. There is good agreement between experimental and theoretical absorption spectra.