Using tunable vacuum–ultraviolet radiation from a synchrotron, the decay pathways of the valence electronic states of in the range 10–25 eV have been determined by threshold photoelectron–photoion coincidence spectroscopy. The ions are separated by a linear time-of-flight mass spectrometer. Coincidence spectra are recorded continuously as a function of energy, allowing threshold photoelectron spectra and yields of the fragment ions to be obtained. At fixed photon energies, spectra are recorded with improved time resolution, allowing the mean total translational kinetic energy, into some dissociation channels to be determined. By comparing the values for single-bond fragmentations 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. The excited states of all three parent cations show some evidence for isolated-state behavior. With and this is apparent from the form of the ion yields in the range 11–15 eV, whereas interpretation of the yields for is hampered by an absence of thermochemical data. New upper limits at 298 K for the enthalpies of formation of and are obtained. At higher photon energies, smaller fragment ions are formed following cleavage of more than one bond. With and 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 the one ion unambiguously assigned, can only form at certain energies with molecular neutral fragments (i.e., involving simultaneous bond-breaking and bond-making processes. The values for cleavage of a single C–F or C–X bond suggest a relationship between the part of the molecule where ionization occurs and the bond that breaks; impulsive values of are more likely to be obtained when the breaking bond lies close to the part of the molecule from which ionization occurs, statistical values when ionization occurs further away from the breaking bond. Furthermore, for all cations there is a trend from impulsive to statistical behavior as the photon energy is increased.
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1 March 2001
Research Article|
March 01 2001
Fragmentation of the valence states of and studied by threshold photoelectron–photoion coincidence spectroscopy
D. P. Seccombe;
D. P. Seccombe
School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
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R. P. Tuckett;
R. P. Tuckett
School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
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B. O. Fisher
B. O. Fisher
Department of Physics, University of Reading, Whiteknights, Reading RG6 2AF, United Kingdom
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J. Chem. Phys. 114, 4074–4088 (2001)
Article history
Received:
August 08 2000
Accepted:
December 08 2000
Connected Content
This is a companion to:
Vacuum–ultraviolet absorption and fluorescence spectroscopy of and in the range 8–22 eV
Citation
D. P. Seccombe, R. P. Tuckett, B. O. Fisher; Fragmentation of the valence states of and studied by threshold photoelectron–photoion coincidence spectroscopy. J. Chem. Phys. 1 March 2001; 114 (9): 4074–4088. https://doi.org/10.1063/1.1344889
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