@inbook{82782f6e3d5a4e66a74fffcaeea11219,
title = "CHAPTER 10: Ultrafast Photochemical Reaction Trajectories Revealed by X-ray Transient Absorption Spectroscopy Using X-ray Free Electron Laser Sources",
abstract = "Ultrafast excited state structural dynamics of transition metal complexes have been recently studied at X-ray free electron laser (XFEL) sources that provide X-ray pulses with extraordinary photon flux and tens of femtosecond (fs) pulse durations. In this chapter, a recent study is used as an example to demonstrate that such new light sources can help in resolving electronic configurations for initial excited states before thermalization on the time scale of 100 fs or shorter. Ultrafast X-ray absorption near edge structure (XANES) spectra at the Ni K-edge for the excited states of Ni(ii) tetramesitylporphyrin (NiTMP) before thermalization were measured at the Linac Coherent Light Source (LCLS) by X-ray transient absorption (XTA) using fs laser and X-ray pulses for the {"}pump-probe{"} approach. An excited state evolved from the Franck-Condon state is captured via the experimentally observed red-shifted 1s → 4pz feature and obeys an inverted kinetics with 1 ps rise and 0.3 ps decay time constants. Calculated XANES transitions for these excited states assign a short-lived transient signal to a transiently reduced Ni(i) (π, 3dx2-y2) center resulting from intramolecular charge transfer on a timescale that has eluded previous synchrotron studies. These combined results can be used to extract excited state structural dynamics before thermalization and to capture intermediates of potential photocatalytic significance.",
author = "Chen, {Lin X.}",
note = "Funding Information: We acknowledge support for this work from the Solar energy Photochemistry program (experimental work) and Ultrafast Initiative (theoretical work) of the U. S. Department of energy, Office of Science, Office of Basic energy Sciences, through Argonne National Laboratory under Contract No. De-AC02-06Ch11357 and MLS is supported by the National Institute of health, under Contract No. R01-GM115761 (LXC) and R01-hL63203 (BMh). Use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the U.S. Department of energy, Office of Science, Office of Basic energy Sciences under Contract No. De-AC02-76SF00515. Computations on modeled spectra were facilitated through the use of advanced computational, storage and networking infrastructure provided by the hyak supercomputer system at the University of Washington, funded by the Student technology Fee. PJL is also grateful for support by the State of Washington through the University of Washington Clean energy Institute. MLS also thanks the National Institute of General Medical Sciences of NIh for support through the Molecular Biophysics training grant administered by Northwestern University (5t32 GM008382). Kh gratefully acknowledges support from DANSCAtt and from the Villum and Carlsberg Foundations. the authors would like to thank tim Brandt Van Driel for invaluable assistance with the phase cavity timing correction by providing a means to calibrate the phase cavity data. Publisher Copyright: {\textcopyright} The Royal Society of Chemistry 2017.",
year = "2017",
doi = "10.1039/9781782624097-00201",
language = "English (US)",
series = "RSC Energy and Environment Series",
publisher = "Royal Society of Chemistry",
number = "18",
pages = "201--224",
editor = "Uwe Bergmann and Yachandra, {Vittal K.} and Junko Yano",
booktitle = "Thermoelectric Materials and Devices",
edition = "18",
}