Low-lying electronic structure of EuH, EuOH, and EuO neutrals and anions determined by anion photoelectron spectroscopy and DFT calculations.

The anion photoelectron (PE) spectra of EuH(-) and the PE spectrum of overlapping EuOH(-) and EuO(-) anions are presented and analyzed with supporting results from density functional theory calculations on the various anions and neutrals. Results point to ionically bound, high-spin species. EuH and EuOH anions and neutrals exhibit analogous electronic structures: Transitions from (8)Σ(-) anion ground states arising from the 4f(7)σ(6s)(2) superconfiguration to the close-lying neutral (9)Σ(-) and (7)Σ(-) states arising from the 4f(7)σ(6s) superconfiguration are observed spaced by an energy interval similar to the free Eu(+) [4f(7)6s] (9)S - (7)S splitting. The electron affinities (EAs) of EuH and EuOH are determined to be 0.771 ± 0.009 eV and 0.700 ± 0.011 eV, respectively. Analysis of spectroscopic features attributed to EuO(-) photodetachment is complicated by the likely presence of two energetically competitive electronic states of EuO(-) populating the ion beam. However, based on the calculated relative energies of the close-lying anion states arising from the 4f(7)σ(6s) and 4f(6)σ(6s)(2) configurations and the relative energies of the one-electron accessible 4f(7) and 4f(6)σ(6s) neutral states based on ligand-field theory [M. Dulick, E. Murad, and R. F. Barrow, J. Chem. Phys. 85, 385 (1986)], the remaining features are consistent with the 4f(6)σ(6s)(2) (7)Σ(-) and 4f(7)σ(6s) (7)Σ(-) anion states lying very close in energy (the former was calculated to be 0.15 eV lower in energy than the latter), though the true anion ground state and neutral EA could not be established unambiguously. Calculations on the various EuO anion and neutral states suggest 4f-orbital overlap with 2p orbitals in species with 4f(6) occupancy.