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Fragmentation of valence electronic states of CHF2CF3+ studied by threshold photoelectron–photoion coincidence (TPEPICO) techniques in the photon energy range 12–25 eV

By W. Zhou, D. P. Seccombe, R. P. Tuckett and M. K. Thomas

Abstract

Vacuum ultraviolet synchrotron radiation and threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy have been used to study the decay dynamics of the valence electronic states of CHF\(_2\)CF\(_3^+\). The threshold photoelectron spectrum (TPES) and ion yield curves of the observed fragments have been recorded in the photon energy range 12-25 eV. Electrons and ions are detected by threshold electron analysis and time-of-flight mass spectrometry, respectively. Using a combination of the measured TPES and ab initio molecular orbital calculations, we conclude that the CHF\(_2\)CF\(_3^+\) cation adopts a staggered C\(_s\) geometry, the \(X\)~ \(^2\)A' ground state being formed by electron removal from the 18a' -bonding orbital of CHF\(_2\)CF\(_3\). Upon ionisation, large geometry changes and broad spectral bands are both predicted and observed. The next outer-valence orbitals of CHF\(_2\)CF\(_3\), 17a' and 11a", are predominantly associated with fluorine 2p orbitals located on the CHF\(_2\) group. Translational kinetic energy releases are determined from fixed-energy TPEPICO-TOF spectra. The ground state of CHF\(_2\)CF\(_3^+\) dissociates through CC bond cleavage with a relatively small release of energy. By contrast the \(A\)~ and \(B\)~ states dissociate rapidly by an impulsive mechanism with a larger fractional release of energy to CHFCF\(_3^+\) + F. Upper limits for the ionization threshold of CHF\(_2\)CF\(_3\) (12.70 \(\pm\) 0.05 eV) and the enthalpy of formation of CHFCF\(_3^+\) at 298 K (299 \(\pm\) 7 kJ mol-1, respectively) are determined

Topics: QD Chemistry
Year: 2002
DOI identifier: 10.1016/S0301-0104(02)00790-5
OAI identifier: oai:eprints.bham.ac.uk:682

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