SPECTRAL MOMENTS OF COLLISION-INDUCED ABSORPTION OF CO2 PAIRS - THE ROLE OF THE INTERMOLECULAR POTENTIAL

In this paper we examine the role of the anisotropy of the intermolecu lar potential in the rototranslational collision-induced absorption of the CO2 pairs. Using newly developed formulas [Borysow and Moraldi, P hys. Rev. Lett. 68, 3686 (1992); Moraldi, Phys. Rev. A (submitted)] th at include the effects of anisotropy of the potential to all orders, w e calculate the two lowest spectral moments gamma(1) and alpha(1) for four different classes of CO2 pair potentials and compare the results with the experimental values. We assumed only multipolar induction in the process of forming the induced dipole, with the second-order contr ibutions included. Using a site-site LJ [Murthy et al., Mel. Phys. 50, 531 (1983)] and a site-site semi-ab initio [Bohm, Moi. Phys. 56, 375 (1985)] intermolecular potentials we were able to reproduce the experi mental values of gamma(1) and alpha(1) moments over entire temperature range from 230 to 330 K. Also, the role of an electrostatic interacti on between two CO2 molecules and its impact on the spectral moments is thoroughly investigated. An isotropic core with a point quadrupole ce ntered at each molecule is shown to be an inadequate representation of the CO2-CO2 potential. Additionally, we show the results obtained wit h the first- and second-order perturbation theory to be more than twic e too small.