The mutual neutralization of hydronium and hydroxide.

Bogot, Alon; Poline, Mathias; Ji, MingChao; Dochain, Arnaud; Simonsson, Ansgar; Rosén, Stefan; Zettergren, Henning; Schmidt, Henning T et al. · Science · 2024

basic_science · Level V

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Abstract

Mutual neutralization of hydronium (H<sub>3</sub>O<sup>+</sup>) and hydroxide (OH<sup>-</sup>) ions is a very fundamental chemical reaction. Yet, there is only limited experimental evidence about the underlying reaction mechanisms. Here, we report three-dimensional imaging of coincident neutral products of mutual-neutralization reactions at low collision energies of cold and isolated ions in the cryogenic double electrostatic ion-beam storage ring (DESIREE). We identified predominant H<sub>2</sub>O + OH + H and 2OH + H<sub>2</sub> product channels and attributed them to an electron-transfer mechanism, whereas a minor contribution of H<sub>2</sub>O + H<sub>2</sub>O with high internal excitation was attributed to proton transfer. The reported mechanism-resolved internal product excitation, as well as collision-energy and initial ion-temperature dependence, provide a benchmark for modeling charge-transfer mechanisms.