Intermediate neglect of differential overlap spectroscopic studies of lanthanide complexes: Diatomic lanthanide oxides PrO and TmO

The low-lying states of PrO and TmO arising from the atomic-like molecular ground states 4f²6s and 4f¹²6s, respectively, are calculated employing a spectroscopic intermediate neglect of differential overlap (INDO) molecular orbital procedure augmented by a double-group configuration interaction (CI) technique which includes spin-orbit interactions. The molecular states closely follow the coupling pattern of the atomic states, as is revealed in a display according to the approximate quantum number J_a characterizing the total angular momentum number of the lanthanide contribution to the leading determinant. Overall agreement with experiment and recent ligand field calculations is very good, especially for the manifold of the lowest-lying multiplet component of PrO (J_f=4). Both theoretical procedures reproduce the experimental ω value for the ground state, 3.5. However, the INDO approach predicts a different ω for the ground state of TmO than do ligand field calculations.