Anisotropic rigid rotor potential energy function for H₂O-H ₂

Abstract

We have calculated the interaction for H2O-H2 at 722 points on a five-dimensional surface where both molecules are treated as rigid rotators and we have fitted the ab initio points to a 48-term angular expansion of products of spherical harmonics and rotation matrices. The resulting potential energy function shows strong angle dependence with a large contribution from electrostatic interactions. When averaged over H2 orientations, the resulting water-atom-like surface is found to have zero crossing and minimum at similar distances to the corresponding H2O-He surface but to be generally more repulsive at short range and more attractive at long range. The isotropic average of the potential has a zero-crossing radius σ=3.05 Å and a well depth ∈=49.5 cm-1 at an intermolecular separation Rm=3.52 Å. © 1994 American Institute of Physics.