Ultra-fast charge migration competes with proton transfer in the early chemistry of H2+

by Furong Wang, Uli Schmidhammer, Aurélien de La Landea and Mehran Mostafavi

Phys. Chem. Chem. Phys., 2017, 19, 2894-2899; doi.org/10.1039/C6CP07013B

Oxidation by the ultra-short lived radical cation of water, H2+, can potentially take place at the interface of water and numerous heterogeneous systems involved in radiation therapy, energy and environmental industries. The oxidation processes induced by H2+ can be mimicked in highly concentrated solutions where the nearest neighbors of H2+ may be molecules other than water. The reactivity of H2+ and D2+ is probed in hydrogenated and deuterated sulfuric acid solutions of various concentrations. The oxidized solute, sulfate radical, is observed at 7 ps and remarkably higher yields are found in deuterated solutions. The isotopic effects reveal the competition between two ultrafast reactions: proton transfer toward H2O (D2O) and electron transfer from HSO4 to H2+ (D2+). Density functional theory simulations decipher the electron transfer mechanism: it proceeds via sub-femtosecond charge migration and is not affected by isotopic substitution. This work definitively demonstrates why direct oxidation triggered by H2+ can be competitive with proton transfer.

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