Chemistry of NO and HNO Molecules with Gas-Phase Hydrated O and OH Ions.

The gas-phase reactions of O (H O) and OH (H O) , n=20-38, with nitrogen-containing atmospherically relevant molecules, namely NO and HNO , are studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and theoretically with the use of DFT calculations. Hydrated O anions oxidize NO and NO to NO and NO through a strongly exothermic reaction with enthalpy of -263±47 kJ mol and -286±42 kJ mol , indicating a covalent bond formation. Comparison of the rate coefficients with collision models shows that the reactions are kinetically slow with 3.3 and 6.5 % collision efficiency. Reactions between hydrated OH anions and nitric oxides were not observed in the present experiment and are most likely thermodynamically hindered. In contrast, both hydrated anions are reactive toward HNO through proton transfer from nitric acid, yielding hydrated NO . Although HNO is efficiently picked-up by the water clusters, forming (HNO ) (H O) NO clusters, the overall kinetics of nitrate formation are slow and correspond to an efficiency below 10 %. Combination of the measured reaction thermochemistry with literature values in thermochemical cycles yields ΔH (O (aq.))=48±42 kJ mol and ΔH (NO (aq.))=-125±63 kJ mol .