Metastable fragment production at the C 1s and O 1s edges of the CO2 molecule

We have studied the dissociation of the CO2 molecule into neutral fragments by observing coincidences between neutral metastable fragments and photoions at photon energies between 250 eV and 600 eV. We attribute the metastable signal to oxygen atoms in the 2s(2)2p(3)(S-4)3s(S-5) state and to fragments in high Rydberg states. Neutral metastable fragments are produced by the dissociation of valence-excited states of CO2+ that are populated by direct photoionization or, more efficiently, by core excitation and ionization followed by Auger decay. Metastable fragments were detected at all C 1s and O 1s single excitations, and their intensity was enhanced particularly just above the O 1s and C 1s ionization thresholds, where the recapture of slow photoelectrons is possible. They were also abundantly created at core-valence double excitations, at the thresholds of O 1s and C 1s in shake-up satellites, and to a lesser extent, also in regions of the photoionization continua where there are no resonances.