Spectral moments of collision-induced absorption of CO < inf> 2 pairs: The role of the intermolecular potential

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In this paper we examine the role of the anisotropy of the intermolecular potential in the rototranslational collision-induced absorption of the CO 2 pairs. Using newly developed formulas [Borysow and Moraldi, Phys. Rev. Lett. 68, 3686 (1992); Moraldi, Phys. Rev. A (submitted)] that include the effects of anisotropy of the potential to all orders, we calculate the two lowest spectral moments γ1 and α1 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 contributions included. Using a site-site LJ [Murthy et al., Mol. Phys. 50, 531 (1983)] and a site-site semi-ab initio [Bohm, Mol. Phys. 56, 375 (1985)] intermolecular potentials we were able to reproduce the experimental values of γ1 and α1 moments over entire temperature range from 230 to 330 K. Also, the role of an electrostatic interaction between two CO2 molecules and its impact on the spectral moments is thoroughly investigated. An isotropic core with a point quadrupole centered at each molecule is shown to be an inadequate representation of the CO2-CO2 potential. Additionally, we show the results obtained with the first- and second-order perturbation theory to be more than twice too small. © 1994 American Institute of Physics 3573.

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The Journal of Chemical Physics