The reactions of Ba+ ions with O2 and H2O

The reactions of Ba+ with O2 and with H2O and of Al+ with O2 have been studied in a double-mass spectrometer system. Primary ions were formed by surface ionization. Thresholds were observed for Ba+(O2, O)BaO+ and for Al+(O2, O)AlO+ which were in agreement with values derived from thermochemical data. The results obtained for Al+(O2, O) AlO+ are in agreement with D°0(Al+–O) = 1.69±0.1 eV. The reactions of Ba+ were complicated by the presence of an excited state Ba+(2D3/2, 5/2), and corrections had to be made for the contribution of this species to the reaction. The corrected results for Ba+(O2, O)BaO+ are in agreement with D°0(Ba+–O) = 4.1±0.2 eV. Ba+(H2O, H)BaOH+, which is exothermic, behaves somewhat like an endothermic reaction, and has small cross sections at ECM<1 eV. The population of the excited states in the beam and their contributions are briefly discussed. Atmospheric implications are also briefly discussed.