Triplet dipoles in the absorption spectra of dense rare gas mixtures. I. Short range interactions

Abstract

A theory is proposed to evaluate the induced-dipole moment occuring when three dissimilar atoms are mutually interacting. Based on the one-effective electron model, the theory predicts that, at short and intermediate distances, the triatomic dipole moment originates from three different processes, namely, overlap, quadrupole-induced, and dipole-induced. These three-body dipoles have then been implemented into a molecular dynamics simulation in order to generate the collision-induced absorption spectra by rare-gas mixtures. For Ar–Kr liquid mixtures, the irreducible three-body contributions to the spectral density are found so important that they exceed two-body contributions. This is due to a profound cancellation between two-body dipoles which does not occur between irreducible three-body dipoles. However, the comparison with experimental data is poor because of a shortcoming of the model calculation which does not take into account long-range dispersion interactions. On the contrary, a quantitative agreement is obtained for the fundamental vibration band of compressed H2 –He mixtures, indicating that exchange overlap, three-body dipoles play the leading role for such light systems.