The electron shuffle: Cerium influences samarium 4f orbital occupancy in heteronuclear Ce–Sm oxide clusters

Abstract

The anion photoelectron (PE) spectra along with supporting results of density functional theory (DFT) calculations on SmO, SmCeO, and SmO (y = 1, 2) are reported and compared to previous results on CeO [M. Ray et al., J. Chem. Phys. 142, 064305 (2015)] and CeO (y = 1, 2) [J. O. Kafader et al., J. Chem. Phys. 145, 154306 (2016)]. Similar to the results on CeO clusters, the PE spectra of SmO, SmCeO, and SmO (y = 1, 2) all exhibit electronic transitions to the neutral ground state at approximately 1 eV eBE. The Sm centers in SmO and SmO neutrals can be described with the 4f6s superconfiguration, which is analogous to CeO and CeO neutrals in which the Ce centers can be described with the 4f 6s superconfiguration (Z = Z - 4). The Sm center in CeSmO, in contrast, has a 4f occupancy, while the Ce center maintains the 4f 6s superconfiguration. The less oxidized Sm centers in both SmO and SmCeO have 4f 6s occupancies. The 4f 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 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 SmO exhibits an unusual photon energy-dependence, and the PE spectrum of SmO 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.

Exotic electronic structures of SmxCe3−xOy (x = 0-3; y = 2-4) clusters and the effect of high neutral density of low-lying states on photodetachment transition intensities

“…This is quite similar to the case already noted in Ref. 74 and will be treated in greater theoretical detail in a future publication and may account for the poor agreement between the molecular orbitals for the anionic and neutral systems discussed above.…”

“…While an accurate description of the electronic structure of these complex clusters and cluster anions is better achieved using complete active space methods, the size of the systems presented below warranted the use of less expensive methodologies, which were found to give helpful qualitative insights into homometallic 72,73 and heterometallic species 74 in previous studies. Calculations on a range of molecular and electronic structures of Sm x Ce 3−x O y (x = 0-3; y = 2-4) anions and neutrals were performed using the unrestricted B3LYP hybrid method within the Gaussian 09 program suite.…”

“…4, which shows the PE spectra of (a) Ce 3 complication arises from energetically competitive 4f 5 and 4f 6 subshell occupancies that emerged from DFT calculations on SmO − . 74 The combination of the ferro-and antiferromagnetic spin coupling between the individual like-and unlike atoms in any species with an Sm center results in a large number of electronic states in a narrow (<0.5 eV) energy interval, as summarized in Tables IV-VI. However, previous computational results on homometallic Ce x O y − clusters did provide useful qualitative insight into the electronic and molecular structures, and we again turn to the computational results to qualitatively underpin spectral interpretation.…”

“…The electronic structures of the trimetallic suboxide clusters in this study are compared and contrasted with species in comparable oxidation states, CeO − and Ce x O y − clusters 72,73 along with Sm 2 O y − and SmCeO y − (y = 1-2) clusters, 74 and SmO − , which was recently studied using slow electron velocity map imaging spectroscopy by Neumark and co-workers. 75 We also present results of density functional theory calculations, which have proven to be qualitatively informative, though with these larger systems, we also identify critical shortcomings of this inexpensive computation approach to exceptionally complex electronic structure calculations.…”

“…This effect was previously observed in the Sm 2 O − and Sm 2 O 2 − spectra. 74 While it is a topic of ongoing theoretical treatment, we consider the new evidence from these spectra that can inform further developments in this treatment.…”