UV-induced dissociation dynamics of bromoform probed by Ultrafast Electron Diffraction

ORAL

Abstract

The UV photochemistry of bromoform is investigated by using mega-electron-volt ultrafast electron diffraction (MeV-UED) to study excited-state dissociation dynamics on femtosecond to picosecond timescales. In previous work, using UV pump – XUV probe transient absorption spectroscopy, it was shown that two timescales dominate the photodissociation dynamics of bromoform, each related to a characteristic timescale for either Br or C/H atomic motion.1 Molecular dynamics simulations identified that two pathways to dissociation may exist: (1) C-Br fission along an approximately CS symmetrical reaction pathway and (2) a minor pathway that forms a transient species containing a carbon-halogen-halogen bond, iso-CHBr3, on a timescale of several hundred femtoseconds. During the first 40 fs of the dominant pathway distortion from C3V to a quasi-planar CHBr2 causes significant changes to the excited state valence structure. The displacement of the heavy Br atoms requires up to 300 fs to form separate Br + CHBr2 products. UED enables a direct probe of the changes in the nuclear degrees of freedom and is complementary to the transient absorption study. Here, we present first results from a recent MeV-UED experiment at SLAC National Accelerator Laboratory, which further elucidate the 266 nm induced photodissociation of bromoform. 1B. W. Toulson et al., Struct. Dyn. 6,054304 (2019)

*This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences, Geosciences and Biosciences Division, through Contract No. DE-AC02-05CH11231.

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Presenters

  • Lars Hoffmann

    • Lawrence Berkeley National Laboratory

Authors

  • Lars Hoffmann

    • Lawrence Berkeley National Laboratory

  • Benjamin W Toulson

    • Lawrence Berkeley National Laboratory

  • Pedro Nunes

    • Department of Physics and Astronomy, University of Nebraska- Lincoln, Lincoln, NE, USA
    • UNIVERSITY OF NEBRASKA LINCOLN
    • SLAC National Accelerator Laboratory
    • University of Nebraska-Lincoln

  • Martin Centurion

    • Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, NE,US
    • University of Nebraska - Lincoln

  • Ming-Fu Lin

    • SLAC - Natl Accelerator Lab
    • SLAC National Accelerator Laboratory

  • Andrew Attar

    • SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
    • SLAC National Accelerator Laboratory

  • Michael Zuerch

    • University of California Berkeley
    • University of California, Berkeley

  • Oliver Gessner

    • Lawrence Berkeley National Laboratory