The electronic structure of thorium monoxide: Ligand field assignment of states in the range 0-5 eV

Configuration interaction ligand field theory (CI LFT) calculations of the electronic energy levels of ThO were performed by treating the molecular electronic states as Th2+ free-ion levels perturbed by the ligand field of O2-. Twenty nine experimentally characterized ThO v = 0 energy levels, together with the energy difference between the v = 0 levels of the Y and W states were fitted using a CI LFT model that included Th2+ 7s(2), 6d7s, 6d(2), 7s7p, 6d7p, 5f7s, and 7p(2) configurations. Predictions from these calculations were used to provide tentative assignments for 171 out of 250 ThO band heads listed by Gatterer et al. [Molecular Spectra of Metallic Oxides, Specola Vaticana (1957)]. Term energies for 30 electronic states have been determined based on these assignments. Subsequently, the CI LFT model was refined by fitting to a set of 59 electronic term energies. The inclusion of CI effects together with integer valence, atomic-in-molecule, ionic bonding ideas reveals atomic energy level patterns that are multiply replicated in the molecular energy level patterns of six Th2+ O2- atomic ion configurations (6d7s, 6d(2), 7s7p, 6d7p, 5f7s, and 7p(2)) revealing the underlying atomic ion structure that gives rise to the complex and seemingly erratic unassigned bands reported in the Vatican Atlas. (c) 2018 Wiley Periodicals, Inc.