Oriented dynamics in van der Waals complexes

The effects of relative orientation on collision and reaction dynamics can be examined by characterizing the unimolecular decay of van der Waals complexes. Most commonly, decomposition is initiated by exciting one of the monomers within a complex, and the relative orientation is defined by the zero-point motions for the intermolecular degrees of freedom. However, if simultaneous excitation of the intermolecular degrees of freedom is achieved, a considerable range of starting configurations may be accessed. We are currently studying I₂-Rg and CN-H₂/D₂ complexes with the goal of using these systems to examine oriented dynamics. For I₂(B)-Ne we have observed excited intermolecular vibrations and the effects of these motions on the predissociation dynamics. The correlation between structure and dynamics suggested by these results can be understood using classical mechanics, but the implications of this model are at variance with accepted ideas about the topology of I₂(B)-Rg potential surfaces. Spectroscopic and theoretical studies of CN-H₂/D₂ indicate that this pre-reactive complex may be used to examine steric effects in the H₂+CN→H+HCN reaction. The complex was characterized using the A-X and B-X electronic transitions. As is often the case for weakly bound systems, the insights provided by high-level theoretical calculations were essential for interpretation of the spectra. The properties of excited intermolecular vibrations of CN-H₂ were predicted as a prelude to studies of the intra-cluster reaction dynamics.