Electronic structure and spectroscopy of the MgO2+ cation

Highly correlated ab initio methods are used to investigate the lowest MgO2+ electronic states. Our computations confirm the existence of the strongly bent (MgO2+X∼2A2) form and the weakly bound l-MgOO+(X∼4Σ-) charge quadrupole complex. For both isomers, the three-dimensional potential energy surfaces (3D-PESs) of their electronic ground states are mapped in internal coordinates not far from their respective equilibrium geometries. Then a set of spectroscopic parameters is derived using second order perturbation theory. The rovibrational spectra are also deduced variationally. One-dimensional cuts of the 3D-PESs of the lowest doublet and quartet electronic states of MgO2+ along the RMgO and ROO stretchings and bending are calculated, covering both the molecular and the asymptotic regions. These curves are used later for discussing the metastability of this cation and to propose a plausible mechanism for the Mg+ + O2 atmospheric ion-molecule reaction.