Issue 11, 2012

Dissociation dynamics of fluorinated ethene cations: from time bombs on a molecular level to double-regime dissociators

Abstract

The dissociative photoionization mechanism of internal energy selected C2H3F+, 1,1-C2H2F2+, C2HF3+ and C2F4+ cations has been studied in the 13–20 eV photon energy range using imaging photoelectron photoion coincidence spectroscopy. Five predominant channels have been found; HF loss, statistical and non-statistical F loss, cleavage of the C–C bond post H or F-atom migration, and cleavage of the C[double bond, length as m-dash]C bond. By modelling the breakdown diagrams and ion time-of-flight distributions using statistical theory, experimental 0 K appearance energies, E0, of the daughter ions have been determined. Both C2H3F+ and 1,1-C2H2F2+ are veritable time bombs with respect to dissociation viaHF loss, where slow dissociation over a reverse barrier is followed by an explosion with large kinetic energy release. The first dissociative ionization pathway for C2HF3 and C2F4 involves an atom migration across the C[double bond, length as m-dash]C bond, giving CF–CHF2+ and CF–CF3+, respectively, which then dissociate to form CHF2+, CF+ and CF3+. The nature of the F-loss pathway has been found to be bimodal for C2H3F and 1,1-C2H2F2, switching from statistical to non-statistical behaviour as the photon energy increases. The dissociative ionization of C2F4 is found to be comprised of two regimes. At low internal energies, CF+, CF3+ and CF2+ are formed in statistical processes. At high internal energies, a long-lived excited electronic state is formed, which loses an F atom in a non-statistical process and undergoes statistical redistribution of energy among the nuclear degrees of freedom. This is followed by a subsequent dissociation. In other words only the ground electronic state phase space stays inaccessible. The accurate E0 of CF3+ and CF+ formation from C2F4 together with the now well established ΔfHo of C2F4 yield self-consistent enthalpies of formation for the CF3, CF, CF3+ and CF+ species.

Graphical abstract: Dissociation dynamics of fluorinated ethene cations: from time bombs on a molecular level to double-regime dissociators

Article information

Article type
Paper
Submitted
05 Dec 2011
Accepted
13 Jan 2012
First published
17 Jan 2012
This article is Open Access

Phys. Chem. Chem. Phys., 2012,14, 3935-3948

Dissociation dynamics of fluorinated ethene cations: from time bombs on a molecular level to double-regime dissociators

J. Harvey, A. Bodi, R. P. Tuckett and B. Sztáray, Phys. Chem. Chem. Phys., 2012, 14, 3935 DOI: 10.1039/C2CP23878K

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