DISSOCIATIVE IONIZATION OF CO BY 22.5-48.5 EV PHOTONS - KINETIC-ENERGY MEASUREMENTS OF FRAGMENT IONS BY COINCIDENCE TIME-OF-FLIGHT MASS-SPECTROMETRY

Coincidence time-of-flight mass spectra of C+ and O+ produced by dissociative ionisation of CO by monochromatised photons have been measured in the energy range 22.5-48.5 eV. Fragment ion peak shapes have been analysed to yield kinetic energy release (KER) distributions as a function of photon energy. In the energy region up to 29 eV, good agreement is obtained between the measured values of KER associated with C+ formation and those expected from recent ab initio calculations of the potential energy curves of excited states of CO+. Paucity of theoretical information on CO+ states which dissociate to C + O+ precludes detailed analysis of O+ peak shapes. C+ + O+ pair formation is observed in a photoion-photoion coincidence spectrum measured at a photon energy (40.8 eV) which lies below the energy of the lowest metastable state of CO2+.