INTERMOLECULAR POTENTIAL AND ROVIBRATIONAL LEVELS OF AR-HF FROM SYMMETRY-ADAPTED PERTURBATION-THEORY

A two-dimensional intermolecular potential energy surface for Ar-HF ha s been calculated using the many-body symmetry-adapted perturbation th eory (SAPT). The H-F distance was kept constant at its equilibrium val ue. The interaction energies have been computed using an spdfg-symmetr y basis optimized for intermolecular interactions. In addition, the di spersion and induction energies have been calculated in a few progress ively larger basis sets to determine the basis set convergence and val idity of the asymptotic scaling of those components. Converged results for the dispersion energy have been obtained by using a large basis s et containing spdfgh-symmetry orbitals. The ab initio SAPT potential a grees well with the empirical H6(4,3,2) potential of Hutson [J. Chem P hys. 96, 6752 (1992)], including a reasonably similar account of the a nisotropy. It predicts an absolute minimum of -207.4 cm(-1) for the li near Ar-HF geometry at an intermolecular separation of 6.53 bohr and a secondary minimum of -111.0 cm(-1) for the linear Ar-FH geometry at a n intermolecular separation of 6.36 bohr. The corresponding values for the H6(4,3,2) potential are -211.1 cm(-1) at an intermolecular separa tion of 6.50 bohr and - 108.8 cm(-1) at an intermolecular separation o f 6.38 bohr. Despite this agreement in the overall potentials, the ind ividual components describing different physical effects are quite dif ferent in the SAPT and H6(4,3,2) potentials. The SAPT potential has be en used to generate rovibrational levels of the complex which were com pared to the levels predicted by H6(4,3,2) at the equilibrium separati on. The agreement is excellent for stretch-type states (to within 1 cm (-1)), while states corresponding to bending vibrations agree to a few cm(-1). The latter discrepancies are consistent with the differences in anisotropies of the two potentials. (C) 1995 American Institute of Physics.