Differentiation of the ground vibrational and global minimum structures in the Ar:HBr intermolecular complex

A fully three-dimensional morphed potential energy surface is reported for Ar:HBr. The morphed potential was obtained from parametrized scaling and shifting transformations of an ab initio potential. The optimum parameters of the morphed potential were determined by a regularized nonlinear least-squares fit to available experimental data. The rovibrational dynamics of the complex were computed using an adiabatic separation of the H-Br intramolecular stretching mode from the intermolecular modes of the system. The ground rovibrational state of the morphed potential was found to have the hydrogen-bound structure Ar-HBr. This state was 10.99 cm(-1) more stable than the corresponding state having the van der Waals structure, Ar-BrH, in agreement with experimental data. However, the global minimum of the morphed potential was found to have the van der Waals structure, Ar-BrH. This structure was 20.9 cm(-1) lower in energy than the local minimum having the hydrogen-bound structure, Ar-HBr. (C) 2001 American Institute of Physics.