HUI LI AND ROBERT J. LE ROY, Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
A three-dimensional, analytic potential energy surface for CO2-He that explicitly incorporates its dependence on the Q3 asymmetric-stretch normal-mode coordinate of the CO2 monomer, has been obtained by least-squares fitting new ab initio interaction energies to a new potential form. The potential energy values were obtained from a supermolecule calculation performed at the CCSD(T) level using an aug-cc-pVQZ basis set supplemented with bond functions, and the full counterpoise correction was applied. These points were fitted to a 3-dimensional generalization of the ``Morse/Long-Range'' potential function form which incorporates theoretically known angle-dependent long-range inverse-power dispersion coefficients. The three-dimensional discrete-variable representation method was employed to calculate the rovibrational eigenvalues, without separating the inter- and intramolecular nuclear motions, and our simulated infrared spectra in 3 region of CO2 is compared with experiment.~ This three-dimensional surface will be used to predict the IR vibrational frequency shifts which have been observed for CO2-(He)N clusters with N up to 20.