Comparative electronic structure of a lanthanide and actinide diatomic oxide: Nd versus U
Titel:
Comparative electronic structure of a lanthanide and actinide diatomic oxide: Nd versus U
Auteur:
KRAUSS, M. STEVENS, W.J.
Verschenen in:
Molecular physics
Paginering:
Jaargang 101 (2003) nr. 1-2 pagina's 125-130
Jaar:
2003-01-10
Inhoud:
Using a modified version of the Alchemy electronic structure code and relativistic pseudopotentials, the electronic structure of the ground and low lying excited states of UO, NdO, and NdO+ have been calculated at the Hartree—Fock (HF) and multiconfiguration self-consistent field (MCSCF) levels of theory. Including results from an earlier study of UO+ this provides the information for a comparative analysis of a lanthanide and an actinide diatomic oxide. UO and NdO are both described formally as M+2O-2 and the cations as M+3O-2, but the HF and MCSCF calculations show that these systems are considerably less ionic due to large charge back-transfer in the π orbitals. The electronic states putatively arise from the ligand field (oxygen anion) perturbed f4, sf3, df3, sdf2, or s2f2 states of M+2 and f3, sf2 or df2 states of M+3. Molecular orbital results show a substantial stabilization of the sf3 or s2f2 configurations relative to the f4 or df3 configurations that are the even or odd parity ground states in the M+2 free ion. The compact f and d orbitals are more destabilized by the anion field than the diffuse s orbital. The ground states of the neutral species are dominated by orbitals arising from the M+2sf3 term, and all the potential energy curves arising from this configuration are similar, which allows an estimate of the vibrational frequencies for UO and NdO of 862 cm-1 and 836 cm-1, respectively. For NdO+ and UO+ the excitation energies for the Ω states were calculated with a valence configuration interaction method using ab initio effective spin—orbit operators to couple the molecular orbital configurations. The results for NdO+ are very comparable with the results for UO+, and show the vibrational and electronic states to be interleaved.
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