Abstract
The anion photoelectron (PE) spectra along with supporting results of density functional theory (DFT) calculations on SmO(-), SmCeO(y)(-), and Sm(2)O(y)(-) (y = 1, 2) are reported and compared to previous results on CeO(-) [M. Ray et al., J. Chem. Phys. 142, 064305 (2015)] and Ce(2)O(y)(-) (y = 1, 2) [J. O. Kafader et al., J. Chem. Phys. 145, 154306 (2016)]. Similar to the results on Ce(x)O(y)(-) clusters, the PE spectra of SmO(-), SmCeO(y)(-), and Sm(2)O(y)(-) (y = 1, 2) all exhibit electronic transitions to the neutral ground state at approximately 1 eV e(-)BE. The Sm centers in SmO and Sm(2)O(2) neutrals can be described with the 4f(5)6s superconfiguration, which is analogous to CeO and Ce(2)O(2) neutrals in which the Ce centers can be described with the 4f 6s superconfiguration (Z(Ce) = Z(Sm) - 4). The Sm center in CeSmO(2), in contrast, has a 4f(6) occupancy, while the Ce center maintains the 4f 6s superconfiguration. The less oxidized Sm centers in both Sm(2)O and SmCeO have 4f(6) 6s occupancies. The 4f(6) subshell occupancy results in relatively weak Sm-O bond strengths. If this extra 4f occupancy also occurs in bulk Sm-doped ceria, it may play a role in the enhanced O(2-) ionic conductivity in Sm-doped ceria. Based on the results of DFT calculations, the heteronuclear Ce-Sm oxides have molecular orbitals that are distinctly localized Sm 4f, Sm 6s, Ce 4f, and Ce 6s orbitals. The relative intensity of two electronic bands in the PE spectrum of Sm(2)O(-) exhibits an unusual photon energy-dependence, and the PE spectrum of Sm(2)O(2)(-) exhibits a photon energy-dependent continuum signal between two electronic transitions. Several explanations, including the high magnetic moment of these suboxide species and the presence of low-lying quasi-bound anion states, are considered.