Observing Solvation Dynamics with Simultaneous Femtosecond X-ray Emission Spectroscopy and X-ray Scattering

Kristoffer Haldrup, Wojciech Gawelda*, Rafael Abela, Roberto Alonso-Mori, Uwe Bergmann, Amélie Bordage, Marco Cammarata, Sophie E. Canton, Asmus O. Dohn, Tim Brandt Van Driel, David M. Fritz, Andreas Galler, Pieter Glatzel, Tobias Harlang, Kasper S. Kjær, Henrik T. Lemke, Klaus B. Møller, Zoltán Németh, Mátyás Pápai, Norbert SasJens Uhlig, Diling Zhu, György Vankó, Villy Sundström, Martin M. Nielsen, Christian Bressler

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

59 Citations (Scopus)

Abstract

In liquid phase chemistry dynamic solute-solvent interactions often govern the path, ultimate outcome, and efficiency of chemical reactions. These steps involve many-body movements on subpicosecond time scales and thus ultrafast structural tools capable of capturing both intramolecular electronic and structural changes, and local solvent structural changes are desired. We have studied the intra- And intermolecular dynamics of a model chromophore, aqueous [Fe(bpy)3]2+, with complementary X-ray tools in a single experiment exploiting intense XFEL radiation as a probe. We monitored the ultrafast structural rearrangement of the solute with X-ray emission spectroscopy, thus establishing time zero for the ensuing X-ray diffuse scattering analysis. The simultaneously recorded X-ray diffuse scattering patterns reveal slower subpicosecond dynamics triggered by the intramolecular structural dynamics of the photoexcited solute. By simultaneous combination of both methods only, we can extract new information about the solvation dynamic processes unfolding during the first picosecond (ps). The measured bulk solvent density increase of 0.2% indicates a dramatic change of the solvation shell around each photoexcited solute, confirming previous ab initio molecular dynamics simulations. Structural changes in the aqueous solvent associated with density and temperature changes occur with ∼1 ps time constants, characteristic for structural dynamics in water. This slower time scale of the solvent response allows us to directly observe the structure of the excited solute molecules well before the solvent contributions become dominant.

Original languageEnglish
Pages (from-to)1158-1168
Number of pages11
JournalJournal of Physical Chemistry B
Volume120
Issue number6
DOIs
Publication statusPublished - 18 Feb 2016

Bibliographical note

Funding Information:
This research was funded by the Deutsche Forschungsgemeinschaft (via SFB925, TPA4), by the European XFEL, the Danish National Research Foundations Centre for Molecular Movies, DANSCATT, the Lend?let Programme of the Hungarian Academy of Sciences, The Swedish Energy Agency (STEM), the Swedish Research Council, the Knut & Alice Wallenberg Foundation, and the Swiss NNCR-MUST. C.B. acknowledges funding from the Hamburg Center for Ultrafast Imaging (University of Hamburg), G.V. and V.S. acknowledge the European Research Council for Grants ERC-StG-259709 and ERC-AdvG-VISCHEM-226136, respectively, and K.H. gratefully acknowledges funding from the Carlsberg and Villum Foundations. Portions of this research were carried out at the LCLS at SLAC National Accelerator Laboratory. LCLS is an Office of Science User Facility operated for the U.S. Department of Energy Office of Science by Stanford University.

Publisher Copyright:
© 2016 American Chemical Society.

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