Exploring Anomalous Photoelectron Angular Distributions in the Photoelectron Spectra of Gd₃O₃^-: Study of Gd₃O₂^- and...

Anion photoelectron (PE) spectra of lanthanide oxide clusters obtained previously have exhibited anomalous photoelectron angular distributions which were attributed to strong PE-valence electron (PEVE) interactions. To further explore this effect, we have obtained the PE spectra of Gd₃O₂^- and Gd₃O₃^-, two clusters that have similarly complex electronic structures but contrasting symmetries. The spectra exhibit manifolds of detachment transitions at similar binding energies in a 0.5 eV window of energy. The electron affinity of Gd₃O₂ is measured to be 1.29 ± 0.05 eV, and that of Gd₃O₃ is 1.31 ± 0.05 eV. As seen in previous studies on lanthanide oxide cluster anions in lower than conventional oxidation states, transitions in spectra obtained lower photon energies are more congested than those obtained with higher photon energy, a signature of strong PEVE interactions. While the detachment transitions have predominantly parallel photoelectron angular distributions (PAD), the PAD varies across the manifold of transitions in the PE spectrum of Gd₃O₃^- in a way that suggests four different subgroups of transitions. Results of calculations on Gd₃O₂^- suggest kite or V-shape structures with antiferromagnetic coupling between one of the 4f⁷ subshells with the two others. Calculations on Gd₃O₃^- more definitively point to ring structures with a nearly isoenergetic ferromagnetically coupled high spin (24-tet) state and a dectet state in which one of the 4f⁷ subshells is antiferromagnetically coupled with the other two. Taking these results as qualitative, we propose that strong mixing between the unperturbed states predicted computationally leads to overlapping transitions with different PADs.