Low-Lying Energy Levels of Magnesium Oxide

The low-lying valence levels of MgO are calculated by the LCAO MO SCF method using an extended basis set, in order to ascertain the nature of the ground state of the molecule. Three configurations were computed ab initio using open-shell variational procedures for the excited states. Term values are obtained from the minima of the computed potential curves together with estimates of correlation energy differences between the configurations. The calculations indicate a closed-shell 1Σ+ ground state but with very low-lying (0.3 eV) 3Π and 3Σ+ levels. The electronic partition function of the molecule is recalculated and hence the published dissociation energy adjusted. D0°(MgO) is lowered by 4.5 kcal mole−1. Possible experimental consequences of the proximity of the triplet states to the ground state are discussed.