Using tunable vacuum-ultraviolet radiation from a synchrotron, the decay pathways of the valence electronic states of CF 2 X 2 + (X=Cl,H,Br) At higher photon energies, smaller fragment ions are formed following cleavage of more than one bond.With CF 2 Cl 2 and CF 2 Br 2 , the appearance energies of the fragment ions are close to the thermochemical energy for production of that ion with neutral atoms, suggesting that these ions form by bond-fission processes only. With CF 2 H 2 , the one ion unambiguously assigned, CFH + , can only form at certain energies with molecular neutral fragments (i.e. CFH + + HF), involving simultaneous bond-breaking and bond-making processes. The t values for cleavage of a single C−F or C−X bond suggest a relationship between the part of the molecule where ionisation occurs and the bond that breaks ; impulsive values of t are more likely to be obtained when the breaking bond lies close to the part of the molecule from which ionisation occurs, statistical values when ionisation occurs further away from the breaking bond. Furthermore, for all CF 2 X 2 + cations there is a trend from impulsive to statistical behaviour as the photon energy is increased.4

The ionization and fragmentation of carbon tetrafluoride excited at the C and F 1s thresholds are studied using soft x-ray excitation, threshold electron spectroscopy and state-selective coincidence techniques. The threshold electron spectra reveal indirect low-energy production from pre-edge resonances, and the structure at the thresholds is attributable to post-collision interaction effects, with some evidence of underlying vibrational structure. The coincidence data allow determination of ion and ion pair yield ratios and deduction of the dissociation pathways and final states for the various channels.

The photoionization of SO 2 has been studied in the photon energy range 160-560 eV using the SRS at Daresbury Laboratory, UK. Threshold photoelectron and total ion-yield spectra are presented in the region of the S 2p and O 1s edges. Ion branching ratios are obtained from threshold photoelectron-photoion coincidence (TPEPICO) data and the detailed dynamics of the fragmentation process determined using the threshold photoelectron-photoion-photoion coincidence (TPEPIPICO) technique. The data are compared with other results at the S 2p edges, and with previous studies of SO 2 in the vacuum ultraviolet spectral region.

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