The influence of intracollisional interference on the dipole spectrum of HD

Abstract

The influence of intracollisional interference on the dipole spectrum of pure HD is investigated within the framework of an adiabatic separation of the relative translational motion and non-mixing of rotational levels. The effect leads to a density dependence of the integrated intensities for the sharp spectral lines. It is found that the large discrepancy between the theoretical and experimental pure rotational dipole moment matrix elements for HD reported in the literature can be interpreted as destructive interference between the allowed and the collision-induced dipoles. Similar calculations for the fundamental band are in excellent agreement with the experimental results for the R1(1) line, but agree less well for the R1(0) line. We interpret this, as well as the asymmetrical line shape, as evidence of rotational level mixing due to anisotropic intermolecular forces.