Abstract
A detailed theoretical analysis of the intensities of the pure rotational (J) transitions in gaseous HD is presented. These transitions all manifest small intracollisional interference effects arising from the cross product of the allowed– and the induced–dipole-moment matrix elements. Using recent ab initio calculations of the induced dipole moment in an HD-HD pair, this interference is found to be constructive for most transitions, thus implying a density-dependent increase in intensity. For the (0) transition, a small but significant additional contribution to the constructive intracollisional interference results from the mixing of rotational levels in a single molecule during collisions. Additionally, because of a near-resonance condition, simultaneous mixing of internal rotational levels in both molecules of a colliding pair leads to a large destructive interference affecting primarily the (2) transition. The present theoretical values of the interference parameter are compared with experimental data and it is concluded that while the low-temperature data are in reasonable accord with the present theoretical results, significant differences still remain both between different experimental determinations, and between theory and experiment for the room-temperature data. Possible theoretical refinements to explain the observed large temperature dependence of the intracollisional interference are discussed briefly.
- Received 7 July 1988
DOI:https://doi.org/10.1103/PhysRevA.38.6185
©1988 American Physical Society