Van der Waals Interaction Potential between Polar Molecules. Pair Potential and (Nonadditive) Triple Potential

Abstract

A unified treatment, based on the method of the fluctuating reaction field, is presented for the van der Waals potential between polar molecules. Only dipolar interactions exclusive of retardation effects are considered. The general formulation is given in terms of frequency-dependent molecular susceptibilities and holds for any finite temperature. It is shown that, under certain restrictive conditions, the generalized potential can be decomposed into three parts representing the three constituents of the van der Waals attraction: dispersion, orientation, and induction. The general formalism is applied to the attraction between two bodies and between three bodies. The dispersive, orientative, and inductive parts of the pair potential are compared with the corresponding potentials of London, Keesom, and Falkenhagen and the (nonadditive) triple dispersive potential with the potential of Axilrod and Teller. Explicit expressions are also given for the (nonadditive) triple orientation and induction potentials. The significance of the results is discussed.