RESONANCES - BRIDGE BETWEEN SPECTROSCOPY AND DYNAMICS

Resonances are metastable, quasibound states of a molecular complex. T hey are formed predominantly by vibrational excitation of a molecular complex above a dissociation threshold. Resonances share a number of f eatures in common with bound states, including the possibility of maki ng spectroscopic assignments of them. Thus, resonances can be viewed a s the bridge between the bound state spectrum, conventionally the doma in of spectroscopy, and the continuum, which is the domain of dynamics . I review a variety of methods from a number of articles to calculate and characterize resonances, with a special focus on resonances in HC O. which have been extensively studied both theoretically and experime ntally. HCO represents an extreme case, where most resonances are isol ated and nonoverlapping. The effect of overall rotation on resonance p ositions and widths of HCO is examined in detail, and I present tests of several approximate treatments of rotation. I also point out the ro le that resonances play in the dynamics of unimolecular reactions, rad ical-radical reactions, and recombination/dissociation reactions, agai n using HCO as the key example. The use of ''reduce dimensionality'' i deas to obtain full dimensional reaction probabilities for a resonance -dominated reaction is illustrated for the OH + CO --> H + CO2 reactio n, with special attention to the role of the ''spectator'' CO-stretch.