Dissociative photoionization study of O2

Dissociative photoionization of O2 is studied by an energy–mass analyzing system and synchrotron radiation. The kinetic energy distribution spectra of the O+ ion fragments and the dissociative photoionization efficiency curves for the O+ fragments with zero and 0.8eV kinetic energies are observed at photon energies from 18.5 to 24.7eV. Two vibrational progressions are observed in the zero kinetic energy O+ spectrum and identified as Rydberg series nsσg (n=4 and 5) converging to the 32Πu ionic state of O2. The spectroscopic constants for these Rydberg states are obtained. Post dissociative autoionizations are observed for the O*(2P)nd″(n=3∼5) atomic states in the zero kinetic energy O+ spectrum. A shape resonance structure for the B2Σ−g ionic state is observed in the 0.8eV kinetic energy O+ spectrum. The related dissociation mechanisms are discussed.