Semiclassical Theory of Spectra and Relaxation in Molecular Gases

Abstract

A theory is given for the rotational band contours in microwave, infrared, and Raman spectra, and for nuclear spin—lattice relaxation times. The results are a generalization of Baranger's impact calculation for atomic spectra. The semiclassical approach makes possible nonperturbative calculations beginning directly from the intermolecular potential. When the rotational lines are well resolved, the results reduce to our previous semiclassical expressions for the widths and shifts of isolated rotational lines. At higher densities the results describe the ``collapse'' or narrowing of the band contour which happens when the rotational lines overlap.