MULTI-PROPERTY PREDICTIONS FROM RECENT HE-CO POTENTIAL-ENERGY SURFACES AND RELATED COMMENTS ON THE NATURE OF HETERONUCLEAR RARE-GAS INTERACTIONS

Recently two potential energy surfaces, an empirical potential V-(3,V- 3,V-3) and a potential of the exchange-Coulomb (XC) form, have been de termined by fitting their adjustable parameters to the observed line p ositions of the same high resolution infra-red spectra of He-CO. Both yield results for the IR spectra in excellent agreement with experimen t and with each other but, interestingly, there are significant differ ences between the XC and V-(3,V-3,V-3) potentials as a function of rel ative orientation and interspecies distance for all regions of configu ration space, and not just for the repulsive walls. In this paper seve ral properties of the He-CO dimer, second virial, binary diffusion and shear viscosity (both interaction and mixture) coefficients, are used to discriminate between XC, V-(3,V-3,V-3) and several other literatur e potentials. The explicit calculations of the transport properties ar e carried out in the Mason-Monchik approximation and then scaled to gi ve good estimates of close coupling/classical trajectory results. Comp arison with experiment indicates that the XC potential is currently th e preferred potential energy surface for He-CO. It is emphasized also that the properties obtained from the XC and V-(3,V-3,V-3) surfaces ar e similar, much more similar than a comparison of the potentials would indicate. The reasons for this are discussed, using in part compariso ns of the cross-sections relevant to viscomagnetic effects and to the pressure broadening of depolarized Rayleigh light scattering, which we re calculated for XC and V-(3,V-3,V-3). The effects responsible will n ot occur for the interaction of a rare gas with a homonuclear diatomic molecule and illustrate the difficulty inherent in determining the re lative reliability of potential energy functions for interactions invo lving heteronuclear diatomic molecules.