Predissociation of the d 1Πg Rydberg state in O2: Nature of the Rydberg–valence interactions

Predissociation of the higher vibrational states (v=4–8) of the d 1Πg Rydberg state is investigated experimentally using translational spectroscopy. These states predissociate to the O(1D)+O(1D) dissociation limit. Individual rotational levels of the v=4 state are observed for the first time, and the energies and rotational constants for both 16O2 and 18O2 isotopes are established. The observed predissociation behavior and natural linewidths are explained by invoking both Rydberg–valence and valence–valence interactions. The nearly diabatic nature of the 1 1Πg and 2 1Πg valence states is deduced from these observations. One of the‘‘diabatic’’ valence states is ‘‘bound,’’ and its perturbations on the v=1 to 3 of the Rydberg state explain observations reported from resonance enhanced multiphoton ionization experiments.