A two-dimensional study of the autoionizing decay routes of Rydberg states converging on the ionization threshold in

The autoionizing decay pathways of the five-dipole allowed Rydberg series converging on the threshold in have been investigated using two-dimensional photoelectron spectroscopy. Measurements of electron yield as a function of both electron and photon energy have been carried out using tuneable synchrotron radiation. The vast majority of vibrational levels of the three bound electronic states of the ion that are accessible to the decaying Rydberg states have been studied with an experimental resolution of approximately 30 meV. This was sufficient to study transitions to individual vibrational levels. The comprehensive nature of the data presented has enabled various observations pertaining to both electronic and vibrational selectivity in the autoionizing decay processes to be made. The observed preference for the decay of and Rydberg states to the and states of the ion respectively may be explained if the emitted electron conserves its angular momentum. Members of the series result in the most intense features in the spectrum of the only available ion state that has a nuclear arrangement which is significantly different from that of the autoionizing states. It appears that dissociative, neutral states are more likely to be accessed from states and it seems plausible that these dissociative states play a role in the resonant population of the state. There is also evidence to suggest that this state has a bent equilibrium geometry.