Magnesium- and calcium-containing molecular dications: a high-level theoretical study

High-level ab initio quantum chemical calculations, using the GAUSSIAN-2 (G 2), G2(MP2), and G2(QCI) procedures, are reported for the species MX2+ (M = Mg and Ca; X = NH3, H2O, HF, PH3, H2S, HCl, CO, and N-2). In most instance s, these molecular dications are predicted to be thermodynamically stable w ith respect to the lowest energy dissociation products. For M(CO)(2+), the two linear geometries MCO2+ and MOC2+ are both found to represent strongly bound equilibrium structures, with the MCO2+ isomer lying lower in energy. It is hoped that the present thermochemical data may aid in future experime ntal investigations of metal-containing dications. (C) 1999 Elsevier Scienc e B.V.