Doubly positive diatomic molecules

In this, the first of a series of papers dealing with doubly positive diatomic molecules, calculations on the molecule N2 2+ are described. The complete active space SCF (CASSCF) method is used to generate electronic wavefunctions and potential energy curves for a number of bound and unbound N2 2+ states. Spectroscopic constants are obtained from rovibrational energy level calculations for the bound states. Details of the computational methods used are given and the computed results are compared with optical spectroscopy, Auger spectroscopy and mass spectroscopy measurements. The agreement between the CASSCF and experimental results is as good as has been observed for other molecules, yielding spectroscopic constants of semi-quantitative accuracy. Natural orbital analyses of the CASSCF wavefunctions are given, but no simple picture of the origins of the binding in N2 2+ emerges. All the electronic states are shown to be poorly described by a single electronic configuration.