Proton transfer underpins number of chemical and biochemical processes, yet its sub-100 fs dynamics have rarely been captured in real time. Here, we report direct and time-resolved observation of ionizing radiation-induced proton transfer in a heteroaromatic hydrate: the pyrrole-water complex. Both the electron-impact and strong-field laser experiments create a locally and doubly charged pyrrole unit (C4H5N2+), which immediately (within 60 fs) donates a proton to the adjacent H2O, generating deprotonated C4H4N+ and hydronium H3O+ cations that subsequently undergo Coulomb explosion. The electron-impact experiments directly revealed initial states and provided dynamical insights through fragment ions and electron coincidence momentum imaging. The strong-field femtosecond laser experiments tracked the ultrafast dynamics of proton transfer; complementary ab initio calculations unraveled the dynamical details. The 50-60 fs proton transfer qualifies as one of the fastest acid-base reactions observed to date. This study offers a novel perspective on radiation-induced proton transfer in hydrated biomolecules.

Federal Research Center A E Favorsky Irkutsk Institute of Chemistry of the Siberian Branch of the Russian Academy of Sciences Favorskogo str 1 664033 Irkutsk Russia

Institute of Atomic and Molecular Physics Jilin University Changchun 130012 China

MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter School of Physics Xi'an Jiaotong University Xi'an 710049 China

University of Chemistry and Technology Department of Physical Chemistry Technická 5 16628 Prague 6 Czech Republic

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