Jump to main content
Jump to site search

Issue 40, 2016
Previous Article Next Article

Direct comparison of 3-centre and 4-centre HBr elimination pathways in methyl-substituted vinyl bromides

Author affiliations

Abstract

Elimination of HBr from UV-photoexcited vinyl bromides can occur through both 3-centre and 4-centre transition states (TSs). The competition between these pathways is examined using velocity map imaging of HBr (v = 0–2, J) photofragments. The three vinyl bromides chosen for study have methyl substituents that block either the 3-centre or the 4-centre TS, or leave both pathways open. The kinetic energy distributions extracted from velocity map images of HBr from 193 nm photolysis of the three vinyl bromide compounds are approximately described by a statistical model of energy disposal among the degrees of freedom of the photoproducts, and are attributed to dissociation on the lowest electronic state of the molecule after internal conversion. Dissociation via the 4-centre TS gives greater average kinetic energy release than for the 3-centre TS pathway. The resonance enhanced multi-photon ionization (REMPI) schemes used to detect HBr restrict measurements to J ≤ 7 for v = 2 and J ≤ 15 for v = 0. Within this spectroscopic range, the HBr rotational temperature is colder for the 4-centre than for the 3-centre elimination pathway. Calculations of the intrinsic reaction coordinates and RRKM calculations of HBr elimination rate coefficients provide mechanistic insights into the competition between the pathways.

Graphical abstract: Direct comparison of 3-centre and 4-centre HBr elimination pathways in methyl-substituted vinyl bromides

Back to tab navigation

Supplementary files

Publication details

The article was received on 03 Aug 2016, accepted on 19 Sep 2016 and first published on 21 Sep 2016


Article type: Paper
DOI: 10.1039/C6CP05393A
Citation: Phys. Chem. Chem. Phys., 2016,18, 28353-28364
  • Open access: Creative Commons BY license
  •   Request permissions

    Direct comparison of 3-centre and 4-centre HBr elimination pathways in methyl-substituted vinyl bromides

    S. Pandit, B. Hornung and A. J. Orr-Ewing, Phys. Chem. Chem. Phys., 2016, 18, 28353
    DOI: 10.1039/C6CP05393A

    This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. Material from this article can be used in other publications provided that the correct acknowledgement is given with the reproduced material.

    Reproduced material should be attributed as follows:

    • For reproduction of material from NJC:
      [Original citation] - Published by The Royal Society of Chemistry (RSC) on behalf of the Centre National de la Recherche Scientifique (CNRS) and the RSC.
    • For reproduction of material from PCCP:
      [Original citation] - Published by the PCCP Owner Societies.
    • For reproduction of material from PPS:
      [Original citation] - Published by The Royal Society of Chemistry (RSC) on behalf of the European Society for Photobiology, the European Photochemistry Association, and RSC.
    • For reproduction of material from all other RSC journals:
      [Original citation] - Published by The Royal Society of Chemistry.

    Information about reproducing material from RSC articles with different licences is available on our Permission Requests page.

Search articles by author

Spotlight

Advertisements