Uranium 5d-5f electric-multipole transitions probed by nonresonant inelastic x-ray scattering

Nonresonant inelastic x-ray scattering (NIXS) experiments have been performed to probe the 5d-5f electronic transitions at the uranium O 4,5 absorption edges in several systems characterized by either a localized or itinerant character of the U5f electrons, namely, UO2, USe, US, and elemental uranium in the α form. For small values of the scattering vector q, the spectra are dominated by dipole-allowed transitions encapsulated within the ill-defined giant resonance, whereas for higher values of q the multipolar transitions of rank k=3 and 5 give rise to strong and well-defined multiplet peaks in the pre-edge region. The origin of the observed nondipole multiplet structures is explained on the basis of many-electron atomic spectral calculations. The results obtained demonstrate the high potential of NIXS as a bulk-sensitive technique for the characterization of the electronic properties of actinide materials. The different U compounds show strong variations in the O5 structure that can be correlated with the ground-state properties of the materials. © 2010 The American Physical Society.