SPECTROSCOPY AND DYNAMICS OF HYDRIDE RADICAL VAN-DER-WAALS COMPLEXES

Complexes consisting of a diatomic hydride radical bound to a rare gas atom (Rg) offer unique opportunities for investigations of weak bonding interactions and predissociation dynamics. Electronic spectra for these complexes typically exhibit progressions in the intermolecular stretch and bending vibrations. Analyses of the energy level structures associated with these large-amplitude motions provide detailed information concerning the intermolecular potential energy surfaces. Subtle aspects of the intermolecular interactions are revealed by the way in which the rotational, vibrational, and electronic angular momenta are coupled. Potential energy surfaces derived from spectroscopic data establish benchmarks against which ab-initio models of open-shell complexes may be tested. The lighter hydride radical complexes are ideal for this purpose, as they are small enough to be treated using rigorous methods. Vibrational and electronic predissociations of complexes are the half-collision analogs of vibrational and electronic energy transfer processes. For OH/D-Rg complexes the dependence of the predissociation dynamics on the electronic and intermolecular vibrational state has been explored. The results illustrate how the depth and anisotropy of the interaction potential influence the rate and mechanism of predissociation. The present article reviews recent studies of OH/D-Rg, SH-Ar, NH-Ar, and CH-Rg complexes. Emphasis is placed on the hydroxyl radical species, as these have been most thoroughly characterized. Data for the other hydride radical complexes are discussed in the light of insights gained from the hydroxyl complexes and results from matrix isolation studies.