Filming the molecular dynamics of acetylacetone with time-resolved x-ray scattering

ORAL

Abstract

Time-resolved x-ray scattering from UV photoexcited acetylacetone was measured at the LINAC Coherent Light Source in February 2020. Using a 266 nm, 42 fs, 5 uJ laser pulse, acetylacetone is excited to the ππ* state. Simulations suggest it subsequently undergoes hydrogen transfer dynamics and internal conversion to a spectroscopically dark nπ* state. The nπ* state further relaxes via intersystem crossing to a triplet ππ* state. Time-resolved x-ray scattering at 15 keV films the acetylacetone dynamics in reciprocal space up to a momentum transfer of 7 inverse Angstroms, which may then be used to recover the real-space electron distribution with 0.89 Angstroms of spatial resolution. The real-space electron distribution is sensitive to the pump-probe delay between the laser and x-ray pulses, and it generates a film strip of the real-space dynamics of acetylacetone with sub-50 fs time-resolution, which may then be compared to simulation. The fine time-resolution enables the generation of film strips in reciprocal-space and reciprocal-time through application of a temporal Fourier transform to the time-resolved x-ray scattering measurement, which provides a state-selective view of the molecular dynamics, for example, vibrations and dissociations may be segregated in this representation. Moreover, this measurement marks the finest temporal resolution (sub-50 fs) at 0.89 Angstroms of Fourier-transform limited spatial resolution in a gas-phase scattering experiment. This is thanks to the recent upgrade of the LCLS undulators, which now provide up to 1 mJ of pulse energy at photon energies around 20 keV.

*This research is supported through the Stanford PULSE Institute, SLAC National Accelerator Laboratory by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical, Geological and Biosciences, Atomic, Molecular, and Optical Science Program. Use of the Linac Coherent Light Source, SLAC National Accelerator Laboratory is supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.

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Presenters

  • Matthew R Ware

    • Stanford Univ
    • Stanford University

Authors

  • Matthew R Ware

    • Stanford Univ
    • Stanford University

  • 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

  • Nanna Holmgaard List

    • SLAC National Accelerator Laboratory
    • Stanford University

  • Martin Centurion

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

  • Thomas J Wolf

    • SLAC - Natl Accelerator Lab
    • SLAC National Accelerator Laboratory
    • SLAC - National Accelerator Laboratory