Anisotropic molecular interactions II. Expansion of pair molecular interaction into the series of Wigner rotation functions

Abstract

Based on the convergent expansion of site-site interaction, a new form of pair molecular interaction is derived. Quite complicated cartesian vector form of interaction is simplified by the transformation to irreducible spherical tensor representation. In this representation the molecular interaction is given by the power series of Wigner rotation functions (WRF)TDμζkDηξl withk, l=0, 2. The irreducible spherical tensor representation can be rewritten to series of WRFTDμζkDηξl which form the orthogonal basis of functions with evenk, l=2n, wheren=1, 2, 3,... ..., ∞. Thanks to the convergence conditions of the site-site interaction it is possible to consider only a limited part of the infinite basis for the correct description of interaction. This experimentally supported reduction cannot be done on the basis of multipole expansion of interaction.