## The electron shuttle: Cerium influences samaraium 4f orbital occupancy in heteronuclear Ce-Sm oxide clusters

The anion photoelectron (PE) spectra along with supporting results of density functional theory (DFT) calculations on SmO$^−$, SmCeO$_y$$^−, and Sm2O_y$$^−$ (y = 1, 2) are reported and compared to previous results on CeO$^−$ [M. Ray et al., J. Chem. Phys. 142, 064305 (2015)] and Ce2O$_y$$^− (y = 1, 2) [J. O. Kafader et al., J. Chem. Phys. 145, 154306 (2016)]. Similar to the results on Ce_xO_y$$^−$ clusters, the PE spectra of SmO$^−$, SmCeOy$^−$, and Sm$_2$O$_y$$^− (y = 1, 2) all exhibit electronic transitions to the neutral ground state at approximately 1 eV e−BE. The Sm centers in SmO and Sm_2O_2 neutrals can be described with the 4f56s superconfiguration, which is analogous to CeO and Ce_2O_2 neutrals in which the Ce centers can be described with the 4f 6s superconfiguration (ZCe = ZSm − 4). The Sm center in CeSmO_2, in contrast, has a 4f6 occupancy, while the Ce center maintains the 4f^{6}6s superconfiguration. The less oxidized Sm centers in both Sm_2O and SmCeO have 4f6 6s occupancies. The 4f6 subshell occupancy results in relatively weak Sm–O bond strengths. If this extra 4f occupancy also occurs in bulk Sm-doped ceria, it may play a role in the enhanced O^{2−} ionic conductivity in Sm-doped ceria. Based on the results of DFT calculations, the heteronuclear Ce–Sm oxides have molecular orbitals that are distinctly localized Sm 4f, Sm 6s, Ce 4f, and Ce 6s orbitals. The relative intensity of two electronic bands in the PE spectrum of Sm_2O^− exhibits an unusual photon energy-dependence, and the PE spectrum of Sm_2O_2$$^−$ 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.

Publication Date:
May 19 2017
Date Submitted:
Feb 22 2019
Citation:
The Journal of Chemical Physics
146