Pressure Broadening as a Prototype of Relaxation

Abstract

The theoretical results of Baranger, Kolb, and Griem on pressure broadening are rederived by a more compact and flexible procedure directly applicable to other relaxation processes. Pressure broadening is worked out to first order in the pressure, including previously disregarded corrections. The procedure adapts the concepts and techniques of scattering theory to the Liouville representation of density matrices. Its key quantity is a frequency-dependent relaxation operator $〈{M}_{c}(\ensuremath{\omega})〉$ introduced by Zwanzig.