SYMMETRY-ADAPTED PERTURBATION-THEORY CALCULATION OF THE AR-H2 INTERMOLECULAR POTENTIAL-ENERGY SURFACE

The many-body symmetry adapted perturbation theory has been applied to compute the Ar-H-2 potential energy surface. Large basis sets containing spd fgh-symmetry orbitals optimized for intermolecular interactions have been used to achieve converged results. For a broad range of the configuration space the theoretical potential energy surface agrees to almost two significant digits with the empirical potential extracted from scattering and infrared spectroscopy data by Le Roy and Hutson. The minimum of our theoretical potential is epsilon(m) = - 164.7 cal/mol and is reached at the linear geometry for the Ar-H-2 distance R(m) = 6.79 bohr. These values agree very well with corresponding empirical results epsilon(m) = - 161.9 cal/mol and R(m) = 6.82 bohr. For the first time such a quantitative agreement has been reached between theory and experiment for a van der Waals system that large. Despite such excellent agreement in the overall potential, the exponential and the inverse R components of it agree to only about 20%.