The knowledge of primary processes following the interaction of high-energy radiation with molecules in liquid phase is rather limited. In the present Perspective, we report on a newly discovered type of relaxation process involving simultaneous autoionization and proton transfer between adjacent molecules, so-called proton transfer mediated charge separation (PTM-CS) process. Within PTM-CS, transients with a half-transferred proton are formed within a few femtoseconds after the core-level ionization event. Subsequent nonradiative decay of the highly nonequilibrium transients leads to a series of reactive species, which have not been considered in any high-energy radiation process in water. Nonlocal electronic decay processes are surprisingly accelerated upon proton dynamics. Such strong coupling of electronic and nuclear dynamics is a general phenomenon for hydrogen-bonded systems, however, its probability correlates strongly with hydration geometry. We suggest that the newly observed processes will impact future high-energy radiation-chemistry-relevant modeling, and we envision application of autoionization spectroscopy for identification of solution structure details.

Department of Physical Chemistry University of Chemistry and Technology Technická 5 16628 Prague Czech Republic

Department of Physics Freie Universität Berlin Arnimallee 14 D 14159 Berlin Germany

Helmholtz Zentrum Berlin für Materialien und Energie Methods for Material Development Albert Einstein Straße 15 D 12489 Berlin Germany

Theoretische Chemie Physikalisch Chemisches Institut Universität Heidelberg Im Neuenheimer Feld 229 D 69120 Heidelberg Germany

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