A simulation study of the induced infrared absorption in liquid CO2

Abstract

A computer-simulation study of the far-infrared absorption in liquid CO₂ is reported. The results are compared with experiment at 273 K. Two intermolecular potential functions were considered. Both were three-site Lennard-Jones plus ideal quadrupolar interactions. In the first, values of the parameters suggested by Murthy et al.(Mol. Phys., 1983, 50, 531) were used; in the second, all size parameters were decreased by 5% from the Murthy values. Induced dipole–induced-dipole time-correlation functions were computed and found to be in reasonable agreement with the function derived from the experimental data. Several models for the induction mechanism were considered, including both distributed dipoles as a representation of the real non-ideal quadrupole moments and an application of the Applequist model for distributed polarizabilities. It was found that the simulated time-correlation functions are significantly altered when one changed from the point quadrupole, point polarizability to any of the ‘distributed’ models. It is concluded that the results are quite sensitive to the size parameter and that values slightly smaller than those of Murthy et al. would give the best effective two-body potential for liquid CO₂.