Electronic structure and spectroscopy of the MgO2+ cation

Highly correlated ab initio methods are used to investigate the lowest MgO2+ electronic states. Our com- putations confirm the existence of the strongly bent (MgO2+(X) over tilde (2)A(2)) form and the weakly bound l-MgOO+ ((X) over tilde4 Sigma(-)) 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 R-MgO and R-OO stretch ings 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+ + O-2 atmospheric ion-molecule reaction. (C) 2008 Elsevier B.V. All rights reserved.