Vibrational resonances in molecular photodissociation: from state-specific to statistical behaviour

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Abstract
We consider resonances in polyatomic molecules induced by coupled vibrational motion on multidimensional potential energy surfaces. The quantities of interest are the resonance positions, their widths as well as the final-state distributions of the products. Depending on the well depth and the strength of the coupling between the internal modes, the resonances can have properties ranging from state- and mode-selective to statistical. For illustration we discuss three generic examples in some detail: (a) the UV photodissociation of XNO molecules with X=F, Cl, CH3O etc; (b) the unimolecular dissociation of HCO in the ground electronic state and (c) the fragmentation of HO2 and NO2 also on their ground-state potential energy surfaces. In the first two cases, the results of ab initio theoretical calculations are related to recent experimental results.