Fourth order intermolecular correlation functions from spectroscopic data and molecular dynamics calculations

The shape of collision induced absorption spectra of noble gas mixtures and the broadening of rotational lines of dipolar molecules dissolved in noble gas fluids are described in terms of time dependent perturbation theory up to fourth order. In combination with second and fourth order intermolecular correlation functions obtained from molecular dynamics calculations, conclusions are made about the importance of these functions for spectroscopic observations. The fourth order correlation functions are highly structured. The form taken by the connected part of the fourth order function depends markedly on the range of the probe interaction.