Ionic fragmentation of K-shell excited and ionized CO

Quantitative ion yields from photoionization of gaseous CO have been measured with time-of-flight mass spectrometry and photoion-photoion coincidence techniques using synchrotron radiation from 270 to 360 eV and from 515 to 615 eV, in the region of C 1s and O 1s excitation and ionization. Dissociative multiple-ionization efficiencies, ion-branching ratios, and the relative yields of all possible ionization reactions are derived. The distributions of kinetic energies released to the (C++O+) and (C2++O+) pairs are measured. Very large contributions of symmetric dissociative double ionization producing C+ and O+ are found, even in the region of the 1s→π* resonances. The results are discussed in the context of the autoionization and Auger electron spectroscopy of core-excited CO and with the aid of recent calculations of the potential curves of CO2+. The relationship between the present results and those for photon-stimulated desorption following core excitation and ionization of solid and chemisorbed CO is explored.