Photodissociation dynamics of state-selected resonances of HCO X̃ ²A′ prepared by stimulated emission pumping

Metastable resonances on the ground electronic state of the HCO radical have been prepared by stimulated emission pumping. The resonances have energies 5000 to 10 000 cm^-1 above the dissociation limit of HCO and can be assigned by their vibrational and asymmetric-top rotational character. The transition linewidths of the resonances and the rotational and vibrational distributions of the CO dissociation products have been measured. The linewidths show a strong dependence on the vibrational character of the resonance rather than a monotonic dependence on energy, and thus provide an important example of nonstatistical behavior. CO(v=2) was produced in the decay of all six resonances studied, while only the three highest energy resonances produced measurable amounts of CO(v=3). CO rotational distributions with population in low-J states, which often showed nonstatistical structure, were characteristic of the products from all the resonances studied. The rotational distributions depend both on the vibrational character of the parent state and on the rotational state prepared in the HCO. The experimental results are compared and contrasted with previous quantum mechanical calculations and analyzed in the context of a modified Franck-Condon model for the dissociation.