Competition between autoionization and dissociation in the [O₂⁺(B ²Σ_g^-)]nl and [O₂⁺(c ⁴Σ_u^- )]nl Rydberg states investigated by photon-induced dissociation to neutral fragments

Formation of fluorescing and metastable fragments from photon-induced dissociation of O₂ has been investigated in the 20.2-21.2 eV and 22.5-25.0 eV photon energy regions under high resolution. The neutral particles are detected using a microchannel plate stack, where electric potentials prevent charged particles from reaching the detector. Yield curves of excited neutral particles exhibit peaks at Rydberg states converging to O₂⁺(B ²Σ_g^-) and O₂⁺(c ⁴Σ_u^-). Furthermore, these yields are strongly enhanced at high-n, enabling the measurement of their energy location and width. A simple model for the decay of the Rydberg states converging to O₂⁺(c ⁴Σ_u^-) based on the competition between autoionization and neutral dissociation is used to describe qualitatively the observed spectrum. The results indicate that the lifetime of the O₂⁺(c ⁴Σ_u^-)v = 0 level is two orders of magnitude longer than that of the O₂⁺(c ⁴Σ_u^-)v = 1 level.