Photoionisation mass spectrometry of O2 in the VUV region

Photoproduction cross sections of molecular oxygen for O2+ and O+ ions in the wavelength region from 1030 to 400 AA have been obtained using a quadrupole mass spectrometer and synchrotron radiation as a continuum light source. Photoionisation and dissociative photoionisation of O2 in the wavelength region from 750 to 400 AA are discussed. In the yield spectra of O2+ and O+, vibrational structures of the b 4 Sigma u- and B 2 Sigma u- states of O2+ are observed and the features are considered to be due to autoionisation and predissociation. In the Rydberg series converging to the c4 Sigma u- (O2+) state, characteristic features of the window-type and asymmetric profiles appear in both the spectra of O2+ and O+.