Branching and anisotropy of barrier tunneling and fluorescent decay in H2. I. Experiment

Photodissociation of quasibound levels in the i ³P_g state of molecular hydrogen is studied using fast-beam photofragment spectroscopy. The molecules dissociate either via molecular fluorescence to a repulsive state or by barrier tunneling followed by atomic fluorescence. We measured the branching between the two pathways and the anisotropy of the photofragment distribution. The branching ratios were calculated from the potential energy curve (see the theoretical treatment given in the following paper [Phys. Rev. A 54, 531 (1996)]). The observed and calculated branching ratios are found to be in good agreement. Small discrepancies can be accounted for by the electronic mixing with neighboring states. The photofragment anisotropy is a diagnostic tool for the dissociation continuum and the lifetime of the excited state. The experimentally found anisotropy parameters corroborate the electronic mixing and also show that the fine and hyperfine structure are resolvable only for the lowest three rotational levels examined.