Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study

Sara H. Gardiner, Tolga N. V. Karsili, M. Laura Lipciuc, Edward Wilman, Michael N. R. Ashfold, Claire Vallance*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

11 Citations (Scopus)
299 Downloads (Pure)

Abstract

The photodissociation dynamics of ethyl bromide and ethyl iodide cations (C2H5Br+ and C2H5I+) have been studied. Ethyl halide cations were formed through vacuum ultraviolet (VUV) photoionization of the respective neutral parent molecules at 118.2 nm, and were photolysed at a number of ultraviolet (UV) photolysis wavelengths, including 355 nm and wavelengths in the range from 236 to 266 nm. Time-offlight mass spectra and velocity-map images have been acquired for all fragment ions and for ground (Br) and spin-orbit excited (Br*) bromine atom products, allowing multiple fragmentation pathways to be investigated. The experimental studies are complemented by spin-orbit resolved ab initio calculations of cuts through the potential energy surfaces (along the RC-Br/I stretch coordinate) for the ground and first few excited states of the respective cations. Analysis of the velocity-map images indicates that photoexcited C2H5Br+ cations undergo prompt C-Br bond fission to form predominantly C2H5+ + Br* products with a near-limiting ` parallel' recoil velocity distribution. The observed C2H3+ + H-2 + Br product channel is thought to arise via unimolecular decay of highly internally excited C2H5+ products formed following radiationless transfer from the initial excited state populated by photon absorption. Broadly similar behaviour is observed in the case of C2H5I+, along with an additional energetically accessible C-I bond fission channel to form C2H5 + I+ products. HX (X = Br, I) elimination from the highly internally excited C2H5X+ cation is deemed the most probable route to forming the C2H4 (+) fragment ions observed from both cations. Finally, both ethyl halide cations also show evidence of a minor C-C bond fission process to form CH2X+ + CH3 products.

Original languageEnglish
Pages (from-to)2167-2178
Number of pages12
JournalPhysical Chemistry Chemical Physics
Volume16
Issue number5
Early online date26 Nov 2013
DOIs
Publication statusPublished - 2014

Keywords

  • PHOTOELECTRON-PHOTOION COINCIDENCE
  • ENERGY RELEASE DISTRIBUTIONS
  • PHOTODISSOCIATION DYNAMICS
  • KINETIC-ENERGY
  • METHYL-IODIDE
  • THERMOCHEMICAL PROPERTIES
  • MULTIPHOTON IONIZATION
  • ELECTRONIC EXCITATION
  • OSCILLATOR-STRENGTH
  • LOSS SPECTROSCOPY

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