Disentangling proton-transfer and fragmentation dynamics of ionized water dimer in energy and time

Radiation chemistry in aqueous biochemical systems induced by ionizing radiation

primarily leads to the ultrafast dynamics of water molecules. The initial

response of aqueous environment to ionizing radiation involves the formation of

hydrated electrons and ultrafast proton transfer, which was recently probed in

the ionized water dimer [1]. However, so far the subsequent fragmentation

pathways into highly reactant intermediates were only explored by molecular

dynamics simulations. We utilized purified molecular beams of water dimer and

strong-field ionization at 800 nm to investigate the early phase of the aqueous

environment ionization. Using velocity map imaging, we revealed that can either

stabilize or undergo fragmentation along more than ten distinct reaction

pathways [2].

To address the ultrafast dynamics of these ion-reaction pathways, we set up a

disruptive-probing [3] pump-probe experiment that enabled us to track the

formation of all the ionic species simultaneously, directly yielding a reaction

network and branching pathways as well as effective reaction-rate constants.

These findings provide crucial insights into the post-ionizing processes in

aqueous environments, with implications for both atmospheric chemistry and

radiation therapy.

[1] K. Schnorr, M. Belina, et int (7 authors), P. Slavíček, and R. Moshammer, Sci. Adv. 9, eadg7864 (2023)

[2] I.S. Vinklárek, H. Bromberger, N. Vadassery, W. Jin, J. Küpper, and S. Trippel, J. Phys. Chem. A 128, 1593 (2024); arXiv:2308.08006 [physics]

[3] B. Jochim, L. DeJesus, and M. Dantus, Rev. Sci. Instrum. 93, 033003 (2022)