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Threshold photoelectron–photoion coincidence spectroscopy study of CHCl2F+, CHClF+2 and CH2ClF+: Steric influence of the chlorine, fluorine and hydrogen atoms

Howle, C. R. and Collins, D. J. and Tuckett, R. P. and Malins, A. E. R. (2005) Threshold photoelectron–photoion coincidence spectroscopy study of CHCl2F+, CHClF+2 and CH2ClF+: Steric influence of the chlorine, fluorine and hydrogen atoms. Physical Chemistry Chemical Physics, 7 (11). pp. 2287-2297. ISSN 1463-9076

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URL of Published Version: http://dx.doi.org/10.1039/b501838b

Identification Number/DOI: doi:10.1039/b501838b

The threshold photoelectron spectrum and threshold photoelectron-photoion coincidence spectra of CHCl\(_2\)F, CHClF\(_2\) and CH\(_2\)ClF are reported in the range 11.3 - 24.8 eV. Tunable photoionizing radiation with a resolution of 0.3 nm is provided from a synchrotron source with a vacuum-UV monochromator. The coincidence spectra are recorded continuously as a function of photon energy, allowing yields of the fragment ions to be obtained. Energetic comparisons suggest that the major products of the titled molecules dissociate in a similar manner at low photon energy, with the parent and first fragment ion, corresponding to cleavage of the weakest bond, appearing at their thermochemical thresholds. The second major ion, corresponding to cleavage of the second weakest bond, is formed ca. 1 eV higher than its predicted threshold, this disparity implying state-selected dissociation. CHCl\(_2\)F and CHClF\(_2\) fragment in a similar manner at higher photon energies, with minor ions formed by the cleavage of three bonds possessing lower appearance energies than fragment ions formed by the cleavage of two bonds. CH\(_2\)ClF displays the more expected behaviour, namely sequential bond cleavage as the photon energy increases. These observations can be rationalised in terms of the height of the barrier on the exit channel, as determined by the steric bulk of the leaving group. For the three titled molecules, mean translational kinetic energy releases have also been measured into the channels involving C-F or C-Cl bond fission. These data infer impulsive dissociations occur at lower energy, with a trend towards statistical behaviour with increasing photon energy. Competition between statistical and impulsive processes is observed, for example C-Cl vs. C-F bond cleavage in CHCl\(_2\)F\(^+\) and CHClF\(_2^+\).

Type of Work:Article
Date:2005 (Publication)
School/Faculty:Schools (1998 to 2008) > School of Chemical Sciences
Department:School of Chemistry
Subjects:QD Chemistry
QC Physics
Institution:University of Birmingham
Copyright Holders:The authors, Royal Society of Chemistry
ID Code:689
Refereed:YES
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