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

Harvey, J. and Bodi, A. and Tuckett, R. P. and Sztáray, B. (2012) Dissociation dynamics of fluorinated ethene cations: from time bombs on a molecular level to double-regime dissociators. Physical Chemistry Chemical Physics, 14. pp. 3935-3948. ISSN 1463-9076 (In Press)

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Identification Number/DOI: 10.1039/C2CP23878K

The dissociative photoionization mechanism of internal energy selected C$$_2$$H$$_3$$F$$^+$$, 1,1-C$$_2$$H$$_2$$F$$_2^+$$, C$$_2$$HF$$_3^+$$ and C$$_2$$F$$_4^+$$ cations have 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=C bond. By modelling the breakdown diagrams and ion time-of-flight distributions using statistical theory, experimental 0 K appearance energies, E$$_0$$, of the daughter ions have been determined. Both C$$_2$$H$$_3$$F$$^+$$ and 1,1-C$$_2$$H$$_2$$F$$_2^+$$ are veritable time bombs with respect to dissociation via HF loss, where slow dissociation over a reverse barrier is followed by an explosion with large kinetic energy release. The first dissociative ionization pathway for C$$_2$$HF$$_3$$ and C$$_2$$F$$_4$$ involves an atom migration across the C=C bond, giving CF–CHF$$_2^+$$ and CF–CF$$_3^+$$, respectively, which then dissociate to form CHF$$_2^+$$ and CF$$_3^+$$. The nature of the F-loss pathway has been found to be bimodal for C$$_2$$H$$_3$$F and 1,1-C$$_2$$H$$_2$$F$$_2$$, switching from statistical to non-statistical behaviour as the photon energy increases. The dissociative ionization of C$$_2$$F$$_4$$ is found to be comprised of two regimes. 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 E$$_0$$ of CF$$_3^+$$ and CF$$^+$$ formation from C$$_2$$F$$_4$$ together with the now well established ∆$$_f$$Hº of C$$_2$$F$$_4$$ yield self-consistent enthalpies of formation for the CF$$_3$$, CF, CF$$_3^+$$, and CF$$^+$$ species.

Type of Work: Article January 2012 (Publication) Colleges (2008 onwards) > College of Engineering & Physical Sciences School of Chemistry QD ChemistryQC Physics University of Birmingham The authors, Royal Society of Chemistry 1006 YES

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