HIGH-RESOLUTION THRESHOLD PHOTOELECTRON AND PHOTOION SPECTROSCOPY OF OXYGEN IN THE 12-50 EV PHOTON RANGE

High resolution threshold photoelectron and photoion spectra of the ox ygen molecule have been measured in the photon energy range 12 50 eV u sing a penetrating field electrostatic analyser and a synchrotron radi ation source. Besides the well known X 2PI(g), a 4PI(u), A 2PI(u), b 4 SIGMA(g)-, B 2SIGMA(g)-, c 4SIGMA(u)- O2+ states, several other series of vibrational structure are observed in the 21-24 eV range. One seri es is interpreted to result, not from an ion state, but from an autoio nization process involving a neutral state and the nuclear continuum o f an ion state. Above 26 eV, three relatively strong features are obse rved at approximately 27.3 eV, 32.5 eV and 39.5 eV, interspersed with several weaker ones. Dissociation processes from some O2+ states have been studied using a threshold photoelectron-photoion coincidence tech nique (TPEPICO). These observations identify the weak, broad feature a t 24.96 eV as the upsilon = 2 level of the C 4SIGMA(u)- state.