The CID spectra of hydrated oxygen ions



A steady production of positive hydrated oxygen molecular ions has been achieved by the introduction of H2O vapour into the ion source of a mass spectrometer under chemical ionization conditions using O2 reagent gas. Collision-induced dissociation, mass-analyzed ion kinetic energy (CID MIKE) spectra (R. G. Cooks, J. H. Beynon, R. M. Caprioli and G. R. Lester, Metastable Ions, Elsevier, Amsterdam, 1973) of the m/z=50 ions, which correspond to the H2O·Omath image ions, show a prominent loss of a water molecule, but no significant hydrogen loss. By contrast, the CID MIKE spectra of the H2Omath image ions obtained under identical conditions indicate an important successive loss of hydrogen and oxygen atoms, giving rise to an intense H2O peak. Conversely, with H2O·Omath image, a relatively loosely-bound adduct of the two stable moieties is indicated, a ‘cluster’ that fragments into its constituents with a preferential charge retention on the species of lower ionization energy.