Near ultraviolet photochemistry of 2-bromo- and 2-iodothiophene: Revealing photoinduced ring opening in the gas phase?

Barbara Marchetti, Tolga N V Karsili, Orla Kelly, Panos Kapetanopoulos, Michael N R Ashfold

Research output: Contribution to journalArticle (Academic Journal)

9 Citations (Scopus)
527 Downloads (Pure)

Abstract

Velocity map imaging methods, with a new and improved ion optics design, have been used to explore the near ultraviolet photodissociation dynamics of gas phase 2-bromo- and 2-iodothiophene molecules. In both cases, the ground (X) and spin-orbit excited (X*) (where X = Br, I) atom products formed at the longest excitation wavelengths are found to recoil with fast, anisotropic velocity distributions, consistent with prompt C-X bond fission following excitation via a transition whose dipole moment is aligned parallel to the breaking bond. Upon tuning to shorter wavelengths, this fast component fades and is progressively replaced by a slower, isotropic recoil distribution. Complementary electronic structure calculations provide a plausible explanation for this switch in fragmentation behaviour-namely, the opening of a rival C-S bond extension pathway to a region of conical intersection with the ground state potential energy surface. The resulting ground state molecules are formed with more than sufficient internal energy to sample the configuration space associated with several parent isomers and to dissociate to yield X atom products in tandem with both cyclic and ring-opened partner fragments.

Original languageEnglish
Article number224303
Number of pages11
JournalJournal of Chemical Physics
Volume142
Issue number22
Early online date9 Jun 2014
DOIs
Publication statusPublished - 14 Jun 2015

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