Translational and rotational effects upon the Rayleigh spectra of ethane

Abstract

The time-correlation functions (tcfs) corresponding to the spectral intensities and band shapes of the Rayleigh spectra for ethane at several densities and a fixed temperature are examined. The usual tcfs are supplemented by second time derivative (STD) tcfs. It is argued that these functions give a much improved description of the relative importance of translation and rotation in determining the spectra. Evaluations of the STD tcfs for a simple two-site model of the ethane molecule plus the dipole-induced dipole (DID) model for the polarizability induction show rather clearly that it is the translational degrees of freedom that are most important in determining the interaction-induced spectra and tcfs. The density dependence of the separate 2-, 3-, and 4-body terms in the STD tcfs is also shown. The most important factors in determining the Rayleigh spectra of ethane under the chosen conditions are deduced from these tcfs.