The electronic structure of neodymium monoxide: Ligand field assignment of states in the range 0–3 eV

[Display omitted] •Electronic states of NdO molecule were treated as Nd2+ ion levels perturbed by O2-.•Ligand field theory assignment of 36 NdO states in the range 0-3 eV was performed.•The integer valence bonding idea reveals atomic energy level patterns of Nd2+ O2-.•Term energies for eight new electronic states of NdO have been determined.•Energy values of NdO from ab initio calculation coincide within accuracy of 8 cm-1. Ligand field theory calculations of energy levels were performed for the neutral neodymium monoxide by treating the molecular electronic states as Nd2+ free-ion levels perturbed by the ligand field of O2–. Thirty six experimentally characterized NdO v = 0 energy levels were fitted using a single-atomic-configuration approximation LFT models that included Nd2+ molecular energy levels with the lowest (maximum Sc, maximum Lc) 4f-core atomic multiplet states of 4 f3(4I)6s, 4f3(4I)5d, 4f3(4I)6p, 4f4(5I), and 4f2(3H)6s2, configurations. Predictions from these calculations were used to provide tentative assignments for 50 NdO bands reported in the literature. Term energies for eight new electronic states of NdO have been determined based on these assignments. The dipole moment for NdO [16.7]3 state and magnetic ge factor determined in Linton et al. (2008) were used to assign this state to the 4f3(4I)6p electronic configuration. The integer valence, atomic-in-molecule, ionic bonding idea reveals atomic energy level patterns that are multiply replicated in the molecular energy level patterns of five Nd2+ O2– atomic ion configurations. This underlying atomic ion structure gives rise to the complex and seemingly erratic unassigned bands reported in the literature. A comparison with ab initio calculations is given. The state symmetries and energy values of 54 levels of NdO 4f3(4I)6s configuration from ab initio calculation reported in Allouche et al. (2006) coincide within accuracy of 8 cm−1 (1σ) with a LFT model when the LFT parameters were allowed to vary.