The electronic structure of the ground and excited states of Mg+2 and Mg2

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Abstract
The ground and excited valence states of Mg+2 and Mg2 are calculated using the multiconfiguration self‐consistent‐field method. The energy curves of the X 1Σ+g, 3Πg, 3Σ+u, 3Πu, 3Σ+g, 1Πg, 1Σu+, 1Πu, and 2 1Σ+gμ states of Mg2 and the 2Σ+u and 2Πμ curves of Mg+2 are obtained for internuclear separations between 4 and 15 bohr. All of the excited states except the 3Πu and 3Σ+g are found to be bound while the ground state is a weakly bound van der Waals molecule. Comparison between the calculated and experimentally known X 1Σ+g and 1Σ+u energy curves shows good agreement for the equilibrium internuclear separation but the calculated De (620 cm−1) for the best approximation of the X 1Σ+g state exceeds the experimental value by about 40%, and the calculated De for the 1Σ+u state is smaller than the experimental value of 9387 cm−1 by about 1800 cm−1. Analysis of the electronic structure of the excimers shows that the triplet states and the 1Πg state are qualitatively described by covalent molecular orbital theory but all of the other bound singlets require more complicated descriptions including covalent configurational mixing, charge transfer, and Rydberg–covalent configuration mixing. Only the 1Πu state can be unambiguously characterized as a charge transfer state. The Mg2 states were calculated to provide a model of the Group II excimer systems, which are candidates for the active media of lasers.