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 bondi ng interactions and predissociation dynamics. Electronic spectra for t hese complexes typically exhibit progressions in the intermolecular st retch and bending vibrations. Analyses of the energy level structures associated with these large-amplitude motions provide detailed informa tion concerning the intermolecular potential energy surfaces. Subtle a spects of the intermolecular interactions are revealed by the way in w hich the rotational, vibrational, and electronic angular momenta are c oupled. Potential energy surfaces derived from spectroscopic data esta blish benchmarks against which ab-initio models of open-shell complexe s may be tested. The lighter hydride radical complexes are ideal for t his purpose, as they are small enough to be treated using rigorous met hods. 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 b een explored. The results illustrate how the depth and anisotropy of t he interaction potential influence the rate and mechanism of predissoc iation. 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 t he other hydride radical complexes are discussed in the light of insig hts gained from the hydroxyl complexes and results from matrix isolati on studies.