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Probing Competing Relaxation Pathways in Malonaldehyde with Transient X-Ray Absorption Spectroscopy

preprint
submitted on 15.02.2020 and posted on 19.02.2020 by Nanna Holmgaard List, Adrian L. Dempwolff, Andreas Dreuw, Patrick Norman, Todd J. Martínez

Excited-state intramolecular hydrogen transfer (ESIHT) is a fundamental reaction relevant to chemistry and biology. Malonaldehyde is the simplest example of ESIHT, yet only little is known experimentally about its excited-state dynamics. Several competing relaxation pathways have been proposed, including internal conversion mediated by ESIHT and C=C torsional motion as well as intersystem crossing. We perform an in silico transient X-ray absorption spectroscopy (TRXAS) experiment at the oxygen K-edge to investigate its potential to monitor the proposed ultrafast decay pathways in malonaldehyde upon photoexcitation to its bright S2(pp*) state. We employ both restricted active space perturbation theory and algebraic diagrammatic construction for the polarization propagator along interpolated reaction coordinates as well as representative trajectories from ab initio multiple spawning simulations to compute the TRXAS signals from the lowest valence states. Our study suggests that oxygen K-edge TRXAS can distinctly fingerprint the passage through the H-transfer intersection and the concomitant population transfer to the S1(np*) state. Potential intersystem crossing to T1(pp*) is detectable from reappearance of the double pre-edge signature and reversed intensities. Moreover, the torsional deactivation pathway induces transient charge redistribution from the enol side towards the central C-atom and manifests itself as substantial shifts of the pre-edge features. Given the continuous advances in X-ray light sources, our study proposes an experimental route to disentangle ultrafast excited-state decay channels in this prototypical ESIHT system and provides a pathway-specific mapping of the TRXAS signal to facilitate the interpretation of future experiments.

Funding

AMOS program within the Chemical Sciences, Geosciences and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

Villum Foundation (Grant No. VKR023371).

Research Unit “Intermolecular and Interatomic Coulombic Decay” (Grant No. FOR 1789).

Heidelberg Graduate School “Mathematical and Computational Methods for the Sciences” (Grant No. GSC 220) funded by the German Research Foundation.

Knut and Alice Wallenberg Foundation (Grant No. KAW-2013.002).

Swedish Research Council (Grant No. 2018-4343).

European Commission through ITN Computational Spectroscopy in Natural Sciences and Engineering (COSINE) (Project No. 765739).

History

Email Address of Submitting Author

nhlist@stanford.edu

Institution

Stanford University

Country

USA

ORCID For Submitting Author

0000-0002-0246-3995

Declaration of Conflict of Interest

None

Exports