Preprint

PUBDB-2026-00564

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Proton transfer and hydronium formation in ionized water

Vinklarek, I. (Corresponding author)CFEL*Extern*DESY* ; Trippel, S.CFEL*XFEL.EU*DESY* ; Belina, M. ; Blum, L.CFEL*Extern* ; Bromberger, H.CFEL*XFEL.EU*DESY* ; Slavicek, P. (Corresponding author)Extern*XFEL.EU* ; Küpper, J. (Corresponding author)CFEL*XFEL.EU*DESY*

2026

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Report No.: arXiv:2602.17505

Abstract: Aqueous radiation chemistry emerges through ultrafast proton transfer and ion-radical formation with unexplored energy-redistribution dynamics steering the subsequent reactions. We performed time-resolved disruptive probing on pure water dimer, $\text{(H}_2\text{O)}_2$, to disentangle the post-ionization reactions. Through kinetic-energy-resolved ion imaging, we unraveled the dynamics in the $\text{(H}_2\text{O)}_2^+$ ground state: at low-energy ($\sim$0.05 eV) ultrafast proton transfer ($\sim$19 fs) is followed by $\text{H}_3\text{O}^++\text{OH}$ fragmentation ($\sim$360 fs). At higher energies, proton transfer becomes hindered ($\sim$60 fs) while the subsequent fragmentation becomes faster ($\sim$210 fs), evolving into coupled dynamics ($>0.15$ eV, $\sim$100 fs). Moreover, we observed $\text{(H}_2\text{O)}_2^+$ stabilization through a Zundel-like motif. This reveals how ion-radical formation in ionized hydrogen-bonded networks shapes reactivity in aqueous dynamics.

Note: Main manuscript - 4 figures, 8 pages; Supplementary materials - 31 figures, 29 pages

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Contributing Institute(s):

1. CFEL-CMI (FS-CFEL-CMI)
2. Uni Hamburg / Experimentalphysik (UNI/EXP)
3. beauftragt von UNI (UNI/CUI)

Research Program(s):

1. 631 - Matter – Dynamics, Mechanisms and Control (POF4-631) (POF4-631)
2. DFG project G:(GEPRIS)390715994 - EXC 2056: CUI: Tiefe Einblicke in Materie (390715994) (390715994)

Experiment(s):

1. Experiments at CFEL

Appears in the scientific report 2026

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