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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.

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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