Use of generalized Langevin theory to describe far infrared absorptions in non-dipolar liquids

Abstract

The Mori continued fraction representation of the Kubo response function, truncated at first order, generates a spectral function which is successful in describing absorptions of non-dipolar liquids in the high microwave and far infrared regions (1–250 cm^–1). There is some evidence that the equilibrium averages [K_o(0) and K₁(0)] inherent in this representation are both intermolecular properties, in contrast to the case of pure dipolar absorption, where K_o(0) is a single molecule property. The correlation function of the derived spectral function is compared and contrasted with that of the extended diffusion model of Gordon. The experimental measurements are also compared with a gas phase model of bimolecular collision-induced absorption, and a “cell” model of the liquid state due to Litovitz and co-workers, both of which are less satisfactory than the generalised Langevin equation.