Probing photochemical reactivity of aromatic carbonyls with time-resolved X-ray absorption spectroscopy at Oxygen K-edge

ORAL

Abstract

We studied UV-induced ultrafast photochemistry of aromatic carbonyls using time-resolved soft X-ray absorption spectroscopy. We focused on the internal conversion and subsequently interplay between the singlet and triplet states leading to the photodissociation of one of the smallest aromatic carbonyls, Acetophenone (C6H5COCH3), via a Norrish Type-I reactions. Our experiment was carried out in LCLS soft X-ray beamline at the TMO experimental end-station, and we make use of the specific sensitivity (resonance transition between core to empty valence orbitals) of near edge X-ray absorption fine structure spectroscopy (NEXAFS) to the electronic character of the excited states (e.g., ππ* and nπ* states). Gas phase acetophenone was excited with a 266 nm pump pulse, followed by the probing of a soft X-ray pulse from the free-electron laser (FEL) around O K-edge (~530 eV). By scanning the X-ray photo energy across the pre-edge and edge region (~520 to 540 eV), we monitored the X-ray absorbance through the measure of Auger-Meitner electron yield together with the photon spectrum. From our measured time-resolved NEXAF spectra, we observed the pre-edge absorption features at early time (<1ps) which are attributed to the transition from the initial populated ππ* to the nπ* state. The subsequent slower features (>10ps) in the spectra indicate the dynamics to the triplet manifolds before dissociation. This work highlights the unique element and site specificity with utilizing X-ray spectroscopy on ultrafast photochemistry.

*This work was supported by the AMOS program within the DOE Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.The experiement was supported under DOE with contracts DE-AC02-05-CH11231 and DE-AC02-76SF00515.

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Presenters

  • Yusong Liu

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

Authors

  • Yusong Liu

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

  • Martin Graßl

    • SLAC National Accelerator Laboratory

  • Alice Green

    • Stanford PULSE Institute
    • Stanford PULSE Institute, Menlo Park, CA, USA

  • Felix Allum

    • Stanford University
    • Stanford PULSE Institute
    • Stanford PULSE Institute, Menlo Park, CA, USA

  • Kurtis D Borne

    • J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS, USA
    • Kansas State University

  • Martin Centurion

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

  • Xinxin Cheng

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

  • Taran Driver

    • SLAC
    • Stanford PULSE Institute, Menlo Park, CA, USA
    • SLAC National Accelerator Laboratory

  • Ruaridh Forbes

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

  • James M Glownia

    • SLAC - Natl Accelerator Lab
    • LCLS, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
    • SLAC National Accelerator Laboratory

  • Erik Isele

    • Stanford PULSE Institute
    • Stanford University

  • Andrei Kamalov

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

  • K. A Larsen

    • SLAC National Accelerator Laboratory
    • Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA

  • Xiang Li

    • LCLS, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
    • SLAC - Natl Accelerator Lab
    • SLAC

  • Ming-Fu Lin

    • SLAC - Natl Accelerator Lab
    • LCLS, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
    • SLAC

  • Razib Obaid

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

  • Adam M Summers

    • SLAC National Accelerator Laboratory
    • LCLS, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
    • SLAC
    • Stanford University

  • Jun Wang

    • Stanford University
    • Stanford University, Menlo Park, CA, USA

  • Thomas Weinacht

    • Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York, USA
    • Stony Brook University

  • James P Cryan

    • SLAC National Accelerator Laboratory
    • Stanford PULSE Institute, Menlo Park, CA, USA

  • Thomas J Wolf

    • SLAC - Natl Accelerator Lab
    • SLAC National Accelerator Laboratory