Classical Theory of Collision-Induced Absorption in Rare-Gas Mixtures

Abstract

Collision-induced far-infrared absorption has been observed experimentally in several rare-gas mixtures. A theoretical calculation of these spectra is carried out using classical radiation theory to determine the emission spectrum and converting to absorption via Kirchhoff's law. Using a simple empirical form to describe the variation of the collision-induced dipole moment with internuclear separation, and assuming straight-line collision paths, an analytic expression is obtained for the spectrum which agrees well with the experiments. Several elementary integrations allow us to compute analytically the correlation function, relaxation time, static dielectric constant, and other invariants of the spectrum.