Dissociative photoionization of 1‑Halogenated silacyclohexanes: Silicon traps the halogen

Andras Bodi*, Katrin Lilja Sigurdardottir, Águst Kvaran, Ragnar Bjornsson, Ingvar Arnason

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

The threshold photoelectron spectra and threshold photoionization mass spectra of 1-halogenated-1-silacyclohexanes, for the halogens X = F, Cl, Br, and I, have been obtained using synchrotron vacuum ultraviolet radiation and photoelectron photoion coincidence spectroscopy. As confirmed by a similar ionization onset and density functional theory molecular orbitals, the ionization to the ground state is dominated by electron removal from the silacyclohexane ring for X = F, Cl, and Br, and from the halogen lone pair for X = I. The breakdown diagrams show that the dissociative photoionization mechanism is also different for X = I. Whereas the parent ions decay by ethylene loss for X = F to Br in the low-energy regime, the iodine atom is lost for X = I. The first step is followed by a sequential ethylene loss at higher internal energies in each of the compounds. It is argued that the tendency of silicon to lower bond angles stabilizes the complex cation in which C2H4 is η2-coordinated to it, and which precedes ethylene loss. Together with the relatively strong silicon−halogen bonds and the increased inductive effect of the silacyclohexane ring in stabilizing the cation, this explains the main differences observed in the fragmentation of the halogenated silacyclohexane and halogenated cyclohexane ions. The breakdown diagrams have been modeled taking into account slow dissociations at threshold and the resulting kinetic shift. The 0 K appearance energies have been obtained to within 0.08 eV for the ethylene loss for X = F to Br (10.56, 10.51, and 10.51 eV, respectively), the iodine atom loss for X = I (10.11 eV), the sequential ethylene loss for X = F to I (12.29, 12.01, 11.94, and 11.86 eV, respectively), and the minor channels of H loss for X = F (10.56 eV) and propylene loss in X = Cl (also at 10.56 eV). The appearance energies for the major channels likely correspond to the dissociative photoionization reaction energy.

Original languageEnglish
Pages (from-to)9188-9197
Number of pages10
JournalJournal of Physical Chemistry A
Volume120
Issue number46
DOIs
Publication statusPublished - 23 Nov 2016

Bibliographical note

Funding Information:
Á.K. is very grateful to the Kantonsspital Baden for medical care after a biking accident suffered during the measurement campaign. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007−2013) under Grant Agreement No. 226716.

Funding Information:
Á.K. is very grateful to the Kantonsspital Baden for medical care after a biking accident suffered during the measurement campaign. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007−2013) under Grant Agreement No. 226716.

Publisher Copyright:
© 2016 American Chemical Society.

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