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Spectroscopic and Structural Probing of Excited-State Molecular Dynamics with Time-Resolved Photoelectron Spectroscopy and Ultrafast Electron Diffraction

Yusong Liu, Spencer L. Horton, Jie Yang, J. Pedro F. Nunes, Xiaozhe Shen, Thomas J. A. Wolf, Ruaridh Forbes, Chuan Cheng, Bryan Moore, Martin Centurion, Kareem Hegazy, Renkai Li, Ming-Fu Lin, Albert Stolow, Paul Hockett, Tamás Rozgonyi, Philipp Marquetand, Xijie Wang, and Thomas Weinacht
Phys. Rev. X 10, 021016 – Published 22 April 2020
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Abstract

Pump-probe measurements aim to capture the motion of electrons and nuclei on their natural timescales (femtoseconds to attoseconds) as chemical and physical transformations take place, effectively making “molecular movies” with short light pulses. However, the quantum dynamics of interest are filtered by the coordinate-dependent matrix elements of the chosen experimental observable. Thus, it is only through a combination of experimental measurements and theoretical calculations that one can gain insight into the internal dynamics. Here, we report on a combination of structural (relativistic ultrafast electron diffraction, or UED) and spectroscopic (time-resolved photoelectron spectroscopy, or TRPES) measurements to follow the coupled electronic and nuclear dynamics involved in the internal conversion and photodissociation of the polyatomic molecule, diiodomethane (CH2I2). While UED directly probes the 3D nuclear dynamics, TRPES only serves as an indirect probe of nuclear dynamics via Franck-Condon factors, but it is sensitive to electronic energies and configurations, via Koopmans’ correlations and photoelectron angular distributions. These two measurements are interpreted with trajectory surface hopping calculations, which are capable of simulating the observables for both measurements from the same dynamics calculations. The measurements highlight the nonlocal dynamics captured by different groups of trajectories in the calculations. For the first time, both UED and TRPES are combined with theory capable of calculating the observables in both cases, yielding a direct view of the structural and nonadiabatic dynamics involved.

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  • Received 13 July 2019
  • Revised 19 February 2020
  • Accepted 5 March 2020

DOI:https://doi.org/10.1103/PhysRevX.10.021016

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Atomic, Molecular & Optical

Authors & Affiliations

Yusong Liu1, Spencer L. Horton1, Jie Yang2,3, J. Pedro F. Nunes5, Xiaozhe Shen2, Thomas J. A. Wolf2,3, Ruaridh Forbes2,3,6,7, Chuan Cheng1, Bryan Moore5, Martin Centurion5, Kareem Hegazy3,4, Renkai Li2, Ming-Fu Lin2, Albert Stolow7,8,9, Paul Hockett9, Tamás Rozgonyi10,11, Philipp Marquetand12,13,14,*, Xijie Wang2,†, and Thomas Weinacht1,‡

  • 1Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
  • 2SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
  • 3Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
  • 4Department of Physics, Stanford University, Stanford, California 94305, USA
  • 5Department of Physics and Astronomy, University of Nebraska–Lincoln, Lincoln, Nebraska 68588, USA
  • 6Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, United Kingdom
  • 7Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario K1N 6N5, Canada
  • 8Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, Ontario K1N 6N5, Canada
  • 9National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada
  • 10Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest 1117 Magyar tudósok körútja 2, Hungary
  • 11Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest, Hungary
  • 12University of Vienna, Faculty of Chemistry, Institute of Theoretical Chemistry, Währinger Straße 17, 1090 Wien, Austria
  • 13Vienna Research Platform on Accelerating Photoreaction Discovery, University of Vienna, Währinger Straße 17, 1090 Wien, Austria
  • 14University of Vienna, Faculty of Chemistry, Data Science at University of Vienna, Währinger Straße 29, 1090 Wien, Austria

  • *philipp.marquetand@univie.ac.at
  • wangxj@slac.stanford.edu
  • thomas.weinacht@stonybrook.edu

Popular Summary

To understand many fundamental processes in physics, chemistry, and biology—such as how organisms cope with molecular damage from sunlight, the basic steps involved in vision, and energy conversion from light—researchers need to be able to follow molecular changes on femtosecond timescales. While much progress has been made on the experimental side, individual techniques typically offer only a limited view of the full dynamics. Here, we combine spectroscopic and structural probes with calculations of the observables to provide a more complete picture of molecular dynamics following the absorption of light.

Specifically, we combine two complementary measurements: ultrafast electron diffraction and time-resolved photoelectron spectroscopy. Each approach to measuring dynamics provides a useful perspective but rarely provides a complete picture on its own. We combine these methods to follow the electronic and nuclear dynamics of the molecule CH2I2 when exposed to UV light.

Our measurements highlight coupled electron-nuclear dynamics that allow for electronic potential energy to be converted into nuclear kinetic energy as well as complicated structural rearrangements of the molecule that involve symmetry breaking, dissociation, rotation, and nonlocal wave-packet dynamics (i.e., the molecule going “two ways at the same time”).

We envision measurements will be more and more combined to yield much greater insight than would be available with either approach alone. Future hardware development could lead to devices that perform both measurements at the same time. We also believe that this work will spur the development of theory and experiment collaborations, particularly in the case where multiple measurements can be performed on the same system.

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Vol. 10, Iss. 2 — April - June 2020

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