Internal dynamics of van der Waals complexes. I. Born–Oppenheimer separation of radial and angular motion

Abstract

An efficient method has been developed for calculating ground state properties of atom–diatomic van der Waals complexes. The wide amplitude bending motion is decoupled from the radial motion in a way analogous to the Born–Oppenheimer separation of electronic and nuclear motion. The treatment furnishes rigorous upper and lower bounds to the ground state energy that are typically ±3 cm−1 for the Ar–HCl surfaces considered. Extensive comparison of this technique with the close-coupling method of Dunker and Gordon [J. Chem. Phys. 64, 354 (1976)] using intermolecular potentials for the Ar HCl complex indicates excellent agreement in the prediction of angular expectation values and rotational constants for the ground state, while realizing an approximate 700-fold reduction in computation time.