Predissociation of H3 n=2 Rydberg states: Product branching and isotope effects

A translational spectroscopy technique is used to obtain predissociation kinetic energy release spectra from the lowest bound states of H3, 2s 2A′1 and 2p 2A″2. These H*3 states are formed in near-resonant electron capture by 3 keV H+3 in Cs vapor. Their ground rovibrational levels are energetically about 1 eV above the H+H+H dissociation limit, thus all levels can yield both H2+H and the three-body products. The spectra contain both three-body and two-body components and are deconvoluted to obtain the branching ratios. Data obtained from two different ion sources show that the three-body/two-body ratio increases with increased rovibrational energy in the H*3. The results are compared to recent theory and with previously reported ratios from dissociative recombination of H+3. The comparison suggests that the ratio increases monotonically with the total electronic and rovibrational energy in the H*3. D*3 predissocation has a similar behavior. The H- and D-atom spectra from the two-body decay of HD*2 show that the ejected H atom is strongly favored on a per-atom basis.