Capture of Hydroxyl Radicals by Hydronium Cations in Water Microdroplets

Despite the high stability of bulk water, water microdroplets possess strikingly different properties, such as presence hydroxyl radicals (OH?) at air–water interface. Previous studies exhibited recombination OH? into H2O2 molecules and capture by oxidizing other molecules. By spraying pure a mass spectrometer, we detected in form (H4O2)+ that is essentially OH??H3O+, radical combined with hydronium cation through hydrogen bonding. We also successfully captured it two scavengers, caffeine melatonin, key oxidation intermediates bear important mechanistic information were seen. It suggested some previous reactions involving should be attributed to OH??H3O+ rather than dimer (H2O?OH2)+.