Nonlocal polarizability densities and the effects of short-range interactions on molecular dipoles, quadrupoles, and polarizabilities

Abstract

Light scattering and absorption processes that are single-molecule forbidden may be observed in compressed gases and liquids, because of interaction-induced distortions of molecular charge distributions. In order to extract information about intermolecular dynamics from line shape studies of "forbidden" spectroscopic processes, it is necessary to determine collision-induced electrical properties as functions of the separations and relative orientations of the interacting molecules. When overlap is not negligible and series expansions valid at long range break down, a model that represents the distribution of polarizable matter in the interacting molecules by means of nonlocal polarizability densities is applicable in computing these properties. In the model the field that induces nonlocal polarization in one molecule is the sum of an external field and the field due to the polarization (permanent, fluctuating, and induced) of the collision partner. With the inclusion of nonlinear response, the model yields accurate expressions for the induction and dispersion contributions to collision-induced dipoles and polarizabilities; exchange effects are additive to lowest order. To first order in the atomic interaction, analytical results are presented for the dipole induced in one hydrogen atom by the approach of a second, the collision-induced pair quadrupole, and the pair polarizability tensor. © 1984 American Institute of Physics.