The effect of LGNG range many-molecule interactions on the absorption spectra of molecular fluids

On the basis of a mean field theory or an extended van der Waals theory of fluids the absorption spectrum of the fluid is obtained in terms of the dynamic susceptibility of the single molecule perturbed by the interactions with neighbouring molecules. It follows that any characteristic absorption line of sufficiently high frequency which is broadened in the bulk fluid by this perturbing effect is furthermore split into bands as a consequence of the resonant transfer of the absorbed energy between molecules via their many-body long range interactions.