Observation of the fastest chemical processes in the radiolysis of water

Z.-H. Loh, G. Doumy, C. Arnold, L. Kjellsson, S. H. Southworth, A. Al Haddad, Y. Kumagai, M.-F. Tu, P. J. Ho, A. M. March, R. D. Schaller, M. S. Bin Mohd Yusof, T. Debnath, M. Simon, R. Welsch, L. Inhester, K. Khalili, K. Nanda, A. I. Krylov, S. Moeller, G. Coslovich, J. Koralek, M. P. Minitti, W. F. Schlotter, J.-E. Rubensson, R. Santra, and L. Young
Science  367, 179 – 182 (2020)

Elementary processes associated with ionization of liquid water provide a framework for understanding radiation-matter interactions in chemistry and biology. While numerous studies have been conducted on the dynamics of the hydrated electron, its partner arising from ionization of liquid water, H2O+, has remained elusive. We use tunable femtosecond soft x-ray pulses from an x-ray free electron laser to directly reveal the dynamics of the valence hole created by strong-field ionization and to track the primary proton transfer reaction giving rise to the formation of OH. The strong, isolated resonance associated with the valence hole (H2O+/OH) enables straightforward detection. QM/MM calculations reveal that the x-ray spectra are sensitive to structural dynamics at the ionization site. We find signatures of hydrated-electron dynamics in the x-ray spectrum.

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