Effect of van der Waals interaction on Raman transitions. I

Abstract

A general expression neglecting intermolecular exchange but not charge interpenetration, is developed for the effective Raman tensor of two interacting molecules. This expression is obtained from the transition dipole moment in second order time-dependent perturbation theory, from which secular terms have been eliminated by an adaption of the method of Orr and Ward (1971, Molec. Phys., 20, 513). The theory is formulated in terms of transition (Raman) and ordinary charge-density susceptibilities of first and second-order. The results are specialized to a pair of nonoverlapping molecules and are expressed in terms of transition (Raman) and ordinary (hyper) polarizabilities. We display explicit expressions for the transition charge-density susceptibilities and polarizabilities, and draw attention to terms which contain the radiation frequency as a factor in the denominator. Such terms are absent in transition polarizabilities which are approximated by the linear term in the normal coordinate expansion of the ordinary polarizability (the Placzek approximation). We compare our results with the previous treatments of the effect of van der Waals interactions on Raman transitions which were based on semi-classical effective field methods, using the Placzek approximation.

Children of Dutch Nazi collaborators

“…47 Eva and Marrie also have similar memories. 48 The liberation was etched into these children's minds as a time of danger. Without German protection it was clear they were unwanted and without rights.…”