Do protons recombine with O2− and CO2− in water clusters?

Abstract Gas phase reactions of O 2 − (H 2 O) m and CO 2 − (H 2 O) m with HCl as well as HNO 3 are studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. HCl and HNO 3 are efficiently taken up by the clusters. In the reactions of O 2 − (H 2 O) m , a characteristic mass change is observed which is consistent with the evaporation of a hydroperoxyl radical HO 2 , most likely formed via proton transfer to O 2 − . Using CO 2 − (H 2 O) m as the ionic reactant, products indicating the formation of HOCO are hardly observed in the HCl reaction. With HNO 3 , however, evidence is found for elimination of HOCO , resulting from proton transfer to CO 2 − , when the clusters have lost almost all water molecules. Thermochemical cycles using literature thermochemistry show that the reactions are exothermic.