Polarized oxygen Kα x-ray absorption and emission spectra, near 530 eV, of a single crystal of Cs2UO2Cl4 are reported. With the aid of density functional theory calculations and the absorption data, the relative energies of the empty molecular orbitals having primarily uranium 5f and 6d character are assigned. The emission spectra give access to the energy of excitations to these orbitals from the various filled valence-shell orbitals. These energies support the conclusion from the optical spectra that valence excitations from the σu occupied valence orbitals occur at substantially lower energies than those from the σg, πg, and πu orbitals. This latter group of molecular orbitals have much larger oxygen-2p character. The participation of the pseudocore 6p shell in the covalent bonding is established directly by the presence of a charge-transfer transition in emission. With the aid of previous work on the polarized uranium L1- and L3-edge absorption spectra, the order of the empty metal-centered antibonding valence orbitals is established as 5fπ<5fσ∼6dδ∼6dσ<6dπ. The greater antibonding character of 6dπ compared with 6dσ can be explained by the relatively small overlap of the latter orbital with oxygen 2p. However, the relative energies of 5fπ and 5fσ cannot be due to differences in overlap and are attributed instead to a strong hybridization between 5fσ and 6pσ. This superposition is confirmed by the linear dichroism in the U L1-edge absorption spectrum.

We have measured the resonant inelastic x-ray scattering (RIXS) spectra at the Cu L3 edge in a variety of cuprates. Exploiting a considerably improved energy resolution (0.8 eV) we recorded significant dependencies on the sample composition and orientation, on the scattering geometry, and on the incident photon polarization. The RIXS final states correspond to two families of electronic excitations, having local (dd excitations) and nonlocal (charge-transfer) character. The dd energy splitting can be estimated with a simple crystal field model. The RIXS at the L3 edge demonstrates here a great potential, thanks to the resonance strength and to the large 2p spin-orbit splitting.

Resonant inelastic x-ray scattering (RIXS) at the L 2,3 edges of 3d transition metal compounds has recently become a high resolution spectroscopic technique thanks to improvements in the instrumentation. We have chosen the prototypical case of NiO to explore the various levels of interpretation applicable to L 3 RIXS spectra of strongly correlated electron systems. Starting from a set of experimental data measured across the Ni L 3 absorption edge with 550 meV combined energy resolution, we analyse the rich spectral structure within an atomic framework. The spectra can be separated into dd and charge transfer excitation regions. The dd excitations can be interpreted and well reproduced within a crystal field model. The charge transfer excitations are analysed through the comparison with calculations made in the Anderson impurity model. A series of parameters belonging to the proposed models (crystal field strength, charge transfer energy, hybridization integrals) can thus be extracted in a very direct and unambiguous way.

Orbital ordering (OO) in the layered perovskite La0.5Sr1.5MnO4 has been investigated using the enhanced sensitivity of soft x-ray resonant diffraction at the Mn L edges. The energy dependence of an OO diffraction peak over the L(2,3) edges is compared to ligand-field calculations allowing a distinction between the influences of Jahn-Teller distortions and spin correlations. The energy dependence of the diffraction peak at the Mn L1 edge is remarkably different from that observed at the Mn K edge.

The resonant inelastic x-ray scattering ͑RIXS͒ of MnO measured with high energy resolution across the L 2,3 absorption edges of Mn is characterized by a very rich spectral structure due to the local electronic excitations. The spectra are dominated by dd and charge transfer excitations, both dipole allowed in the RIXS process. The spectra strongly depend on the energy and polarization of the incident photons. This vast experimental basis allows an accurate determination of the main parameters of theoretical models used to describe highly correlated electron systems like MnO. We show the results for the single impurity Anderson model and the single ion crystal field model and we compare them. Both models reproduce well the dd excitation spectrum, but the former can also predict satisfactorily the charge transfer excitations.

We have investigated the magnetic structure of a Sr2FeMoO6 single crystal by X-ray magnetic circular dichroism at the L2,3 edges of Fe and Mo sites. The spin magnetic moments we find on Fe (3.05µB) and Mo (−0.32µB) give, for the first time, a direct confirmation of their ferrimagnetic ordering. The presence of a finite spin moment on Mo together with only very small orbital moments on both Fe and Mo confirms that the predicted half-metallicity of the Sr2FeMoO6 compound is due to a configuration with five localized d electrons forming a high-spin moment on Fe and one s antiparallel delocalized electron shared between the Mo and the other sites.

We performed bulk-sensitive x-ray absorption (XAS) in the partial fluorescence yield (PFY) mode, and resonant x-ray emission (RXES) measurements of the solid solution Sc (7 at.%):Ce at the Ce L 3 ͑2p → 5d͒ and M 4,5 ͑3d → 4f͒ absorption edges. We deduce an increasing 4f-band hybridization from the ␥-phase stable at room temperature to the low-temperature ␣-Ce, consistent with the "Kondo collapse" scenario for the transition. The enhanced intrinsic resolution of PFY-XAS allows us to resolve the elusive three-peak structure predicted by theory. Thanks to the selective enhancement typical of RXES, we could estimate the small but non-negligible contribution of the f 2 configuration in the hybrid ground state, and its change in the two phases. The linear dichroism effect in the M 4,5 RXES spectra is consistent with the observed hybridization of 4f and conduction states.

Resonant inelastic x-ray scattering ͑RIXS͒ measurements performed jointly across the M 2,3 and L 3 absorption thresholds are used to study CoO local electronic structure and are supported by model calculations. The high-resolution experimental data provide a precise set of parameters to describe the correlated response of valence electrons. The same core-hole independent set of parameters within the single impurity Anderson model is used to describe both the M ͑3p-3d͒ and L ͑2p-3d͒ resonances. This work shows that combining M and L scattering data provides an enhanced contrast view of the spectral weights. Measured M 2,3 -RIXS spectra are observed to be free of charge-transfer or normal fluorescence contributions. Moreover the cross section of M-RIXS final states with change in spin multiplicity is low. Combining this information with L-edge studies establishes an appealing means of making a better separation between on-site and intersite ͑ligand to metal͒ electronic excitations. Experimental and theoretical features specific to RIXS studies performed at M and L edges are summarized as a basis for future studies on complex transition metal compounds.