The Coulomb explosion of the hydrogen molecule, after absorption of a 76 eV photon, has been studied by momentum imaging the two electrons and the two protons. Absolute fully differential cross sections of high statistical quality are obtained. A subset of the overall data, namely, equal electron-energy sharing, is used to investigate the effects of molecular orientation on the photoelectron angular distribution. Departures from the first-order helium-like model are evident in detection geometries where electron-electron correlation is "frozen."

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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

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___________________________________________________________________________Using tunable vacuum-UV radiation from a synchrotron source in the range 10-25 eV, threshold photoelectron -photoion coincidence (TPEPICO) spectroscopy has been used to determine the decay pathways of the valence electronic states of CCl 3 X + (X = F,H,Br). TPEPICO spectra are recorded continuously as a function of photon energy, allowing threshold photoelectron spectra and yields of the fragment ions to be obtained. At fixed photon energies, spectra are also recorded with improved time resolution, allowing total mean translational kinetic energy releases, t , into some dissociation channels to be determined. By comparing t values for single bond-fission processes (i.e. cleavage of a C−Cl or C−X bond) with those predicted for the limiting extremes of a statistical and an impulsive dissociation, information on the nature of the photodissociation dynamics can be inferred. Excited states of all three parent cations show evidence for isolated-state behaviour, and the t values suggest a relationship between the part of the molecule where ionisation occurs and the bond that breaks to form daughter ion + neutral atom products ; impulsive values of t are more likely to be obtained when the breaking bond lies close to the part of the molecule where ionisation occurs, statistical values when ionisation occurs further away from the breaking bond. At higher photon energies, smaller fragment ions are formed following cleavage of more than one bond. With CCl 3 F and CCl 3 Br, the appearance energies of the daughter ions are close to the thermochemical energy for production of that ion with isolated neutral atoms, suggesting strongly that these ions form by bond-fission processes only. With CCl 3 H, at certain energies some fragment ions can only form with molecular neutral fragments (e.g. CCl 2 + + HCl), involving bond-breaking and bond-making processes. It is suggested that this phenomenon is related to the small size of the hydrogen atom, and hence less steric hindrance in a tightly-constrained transition state along the reaction coordinate.