Dynamics of HI photodissociation in the A band absorption via H-atom Doppler spectroscopy

Abstract

The technique of Doppler spectroscopy was used to measure the angular distribution of the H-atoms ejected during the dissociation of isolated HI molecules excited in the A band absorption continuum by a polarized beam of UV radiation. The observables characterizing the dynamics of HI photodissociation were obtained from the Doppler spectra at nine photolysis photo energies throughout the A band. The comparison of these observables with those obtained in previous studies exhibits marked discrepancies, which are shown to be the consequence of HI clusters that were present in the molecular expansion used in a previous study.

The high level of confidence in the precise values of the observables determined in the present study warranted a formal quantum mechanical analysis leading to the determination of the electronic structure of HI in the A band. The parameters of the potential energy curves were obtained for the dissociative states involved in the transitions responsible for A band absorption. These parameters allowed for an extrapolation of the observables between and beyond the discrete values of photolysis photon energies at which experimental measurements were performed, over the whole A band absorption. The assumption of a direct adiabatic dissociation model provided an excellent representation of the experimental observables for this primary process.