Ab initio study of the hypermagnesium Mg2O+ and Mg3O+ cations

The geometries and vibrational frequencies of MgO+, Mg2O+, and Mg3O+ were calculated using high level ab initio and density functional theories. Mg2O+ (D∞h, 2Σg+) is linear while the planar T-shaped (C2v, 2B2) and Y-shaped (C2v, 2A1) Mg3O+ structures are essentially degenerate. MgO+, Mg2O+ and Mg3O+ have dissociation energies of: MgO+, 52.2 kcal/mol (into O + Mg+; Mg2O+, 93.4 kcal/mol (MgO+Mg+; and Mg3O+, 46.8 kcal/mol (Mg2O+ + Mg). Our results agree well with the relative intensities of these cations in the time-of-flight mass spectra reported in a recent experimental study.