Dissociative ionization of CO by 22.5-48.5 eV photons: kinetic energy measurements of fragment ions by coincidence time-of-flight mass spectrometry

Abstract

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) distribution 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⁺.