AB-INITIO STUDY OF VAN-DER-WAALS INTERACTION OF CO2 WITH AR

The ab initio potential energy surface of the ArCO2 cluster is calcula ted using the supermolecular Moller-Plesset perturbation theory (S-MPP T) and dissected into its fundamental components; electrostatic, excha nge, induction, and dispersion energies. The surface contains a single minimum for the perpendicular approach of Ar toward the C atom which has a well depth of similar to 210 cm(-1) at R=6.5 a(0). This value is obtained using an extended basis set supplied with the bond functions and the fourth order supermolecular Moller-Plesset calculations, and is expected to be accurate to within +/-5%. The areas of the surface c orresponding to the collinear approach of Ar to CO2 contain an extende d plateau. The saddle point in this region for R=9.0 a(0) is stabilize d by 117 cm(-1). The analytical pair potential for Ar-CO2 obtained by fitting to the individual interaction components is provided. The thre e-body effects in the related cluster, Ar2CO2, are examined for two co nfigurations of the Ar2CO2 cluster. The overall nonadditivity is domin ated by the three-body dispersion effect; however, the exchange nonadd itivity is the most anisotropic. The sources of this anisotropy are di scussed. (C) 1996 American Institute of Physics.