Six-dimensional calculation of intermolecular states in molecule-large molecule complexes by filter diagonalization: Benzene–H2O

We present an approach toward the dynamically exact calculation of intermolecular states in molecule-large molecule complexes. The approach employs an intermolecular Hamiltonian specifically formulated with the case of molecule-large molecule complexes in mind. In addition, it makes use of filter diagonalization techniques to diagonalize that Hamiltonian. The approach is applied to the calculation of J50 intermolecular states below about 110 cm in the benzene–H2O complex. The results of the calculation are interpreted in terms of five internal rotation states, a doubly degenerate bending mode and a singly degenerate stretching mode, the latter two modes involving the relative translation of the monomer moieties in the complex. The internal rotation states are discussed in the context of the two-dimensional, free internal rotation/water in-plane torsion model of Pribble et al. @J. Chem. Phys. 103, 531 ~1995!#. It is shown that that model is largely successful in identifying the important features of the low-energy benzene–H2O states that involve rotation and/or libration of water. It is also shown, though, that multimode couplings can have major effects on the detailed nature of the intermolecular level structure of the species. © 1999 American Institute of Physics. @S0021-9606~99!00716-3#