AB-INITIO STUDY OF THE LONG-RANGE INTERACTION BETWEEN HE-2( AND H)

A new estimate of the anisotropic long-range potential energy surface for the interaction of He+ (1s S-2) and H-2(X1SIGMA(g)+) has been comp uted using extended atomic basis sets to construct three-configuration self-consistent-field (MCSCF) molecular orbitals for use in a multire ference configuration interaction expansion including all single and d ouble excitations (MRCISD). The most stable geometry is C2v, in agreem ent with earlier studies, but the well depth is found to be 3.15 kcal/ mol at an intermolecular distance of 2.42 angstrom, 57% deeper and 0.2 angstrom smaller, respectively, than the best previous estimate. The ab initio points are fitted to a potential function with correct long- range behavior, suitable for scattering calculations.