The oxidation of sulfides plays an important role in organic and environmental chemistry. In the work by Carlos M. Silva et al. on page 501, a pH-dependent reaction mechanism of dimethyl sulfide oxidation by hydrogen peroxide is elucidated by quantum chemistry calculations. While the OH2− species is unreactive, the H3O2+ ion is elusive, and the true species that is formed in a solution is the H3O+(H2O2)(H2O)2 cluster. This species is highly reactive, and its reaction with dimethyl sulfide leads to the formation of the H3O2+ ion along the reaction pathway. Quantum chemistry calculations predict the pH-rate profile in very good agreement with experimental data.