Electronic structure of americium sesquioxide probed by resonant inelastic x-ray scattering

The Am $5d$-$5f$ resonant inelastic x-ray scattering (RIXS) data of americium sesquioxide were measured at incident photon energies throughout the Am $O_{4,5}$ edges. The experiment was supported by calculations using several model approaches. While the experimental Am $O_{4,5}$ x-ray absorption spectrum of Am$_2$O$_3$ is compared with the spectra calculated in the framework of atomic multiplet and crystal-field multiplet theories and Anderson impurity model (AIM) for the Am(III) system, the recorded Am $5d$-$5f$ RIXS data are essentially reproduced by the crystal-field multiplet calculations. A combination of the experimental scattering geometry and theoretical analysis of the character of the electronic states probed during the RIXS process confirms that the ground state of Am$_2$O$_3$ is singlet $\Gamma_1$. An appearance of the low-intense charge-transfer satellite in the Am $5d$-$5f$ RIXS spectra at an energy loss of $\sim$5.5 eV, suggests weak Am $5f$-O $2p$ hybridization which is in agreement with AIM estimations of the $5f$ occupancy from spectroscopic data in Am$_2$O$_3$ as being 6.05 electrons

The “Avos” phenomenon: a non-censured theatre in the Novosibirsk University, 1975-1976). In: Mosty (The Bridges), Frankfurt, Germany, 2012, 35: 269–301.] [Part 3]

РЕЗЮМЕ В 1975-1976 гг. группа студентов Факультета Естественных Наук Новосибирского университета (Академгородок) умудрилась создать свой неподцензурный маленький театр «Феномен», который успел просуществовать целый сезон. В этих мемуарах бывших актеров, ныне разбросанных по всему миру, тщательно собранных 35 лет спустя, восстановлена подробная история театра. Центральным событием была (видимо, первая) постановка по поэме Андрея Вознесенского «Авось!» в декабре 1975, задолго до знаменитой рок-оперы. ABSTRACT In 1975-1976, a group of science students of the Novosibirsk University (Russia, Siberia) created a small theatre that managed to avoid the official censorship for the entire season. In this memoir, several former actors, now scattered across the world, reconstruct the detailed history of their “Phenomenon” theatre 35 years later. The central event was the (first) staging (December 1975) of Andrey Voznesensky’s long poem “Avos\u27!”, long before the famous rock opera appeared

X-ray spectroscopic study of chemical state in uranium carbides

UC and UMeC₂ (Me = Fe, Zr, Mo) carbides were studied by the high-energy-resolution fluorescence-detected X-ray absorption (HERFD-XAS) technique at the U M₄ and L₃ edges. Both U M₄ and L₃ HERFD-XAS reveal some differences between UMeC₂ and UC; there are differences also between the M₄ and L₃ edge results for both types of carbide in terms of the spectral width and energy position. The observed differences are attributed to the consequences of the U 5f, 6d–4d(3d) hybridization in UMeC₂. Calculations of the U M₄ HERFD-XAS spectra were also performed using the Anderson impurity model (AIM). Based on the analysis of the data, the 5f occupancy in the ground state of UC was estimated to be 3.05 electrons. This finding is also supported by the analysis of U N₄,₅ XAS of UC and by the results of the AIM calculations of the U 4f X-ray photoelectron spectrum of UC

Effect of carbon content on electronic structure of uranium carbides

The electronic structure of UC$_x$ (x = 0.9, 1.0, 1.1, 2.0) was studied by means of x-ray absorption spectroscopy (XAS) at the C K edge and measurements in the high energy resolution fluorescence detection (HERFD) mode at the U M$_4$ and L$_3$ edges. The full-relativistic density functional theory calculations taking into account the Coulomb interaction U and spin-orbit coupling (DFT+U+SOC) were also performed for UC and UC$_2$. While the U M$_4$HERFD-XAS spectra of the studied samples reveal little difference, the U HERFD-XAS spectra show certain sensitivity to the varying carbon content in uranium carbides. The observed gradual changes in the U M$_4$ HERFD spectra suggest an increase in the C 2p-U 5f charge transfer, which is supported by the orbital population analysis in the DFT+U+SOC calculations, indicating an increase in the U 5f occupancy in UC as compared to that in UC. On the other hand, the density of states at the Fermi level were found to be significantly lower in UC$_2$, thus affecting the thermodynamic properties. Both the x-ray spectroscopic data (in particular, the C K XAS measurements) and results of the DFT+U+SOC calculations indicate the importance of taking into account U and SOC for the description of the electronic structure of actinide carbides

Insight into the structure-property relationship of UO2_{2} nanoparticles

Highly crystalline UO$_{2}$ nanoparticles (NPs) with sizes of 2–3 nm were produced by fast chemical deposition of uranium(IV) under reducing conditions at pH 8–11. The particles were then characterized by microscopy and spectroscopy techniques including high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), high-energy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy at the U M$_{4}$ edge and extended X-ray absorption fine structure (EXAFS) spectroscopy at the U L$_{3}$ edge. The results of this investigation show that despite U(IV) being the dominant oxidation state of the freshly prepared UO$_{2}$ NPs, they oxidize to U$_{4}$O$_{9}$ with time and under the X-ray beam, indicating the high reactivity of U(IV) under these conditions. Moreover, it was found that the oxidation process of NPs is accompanied by their growth in size to 6 nm. We highlight here the major differences and similarities of the UO$_{2}$ NP properties to PuO$_{2}$, ThO$_{2}$ and CeO$_{2}$ NPs

Signatures of technetium oxidation states: a new approach

A general strategy for the determination of Tc oxidation state by new approach involving X-ray absorption near edge spectroscopy (XANES) at the Tc L-3 edge is shown. A comprehensive series of Tc-99 compounds, ranging from oxidation states I to VII, was measured and subsequently simulated within the framework of crystal-field multiplet theory. The observable trends in the absorption edge energy shift in combination with the spectral shape allow for a deeper understanding of complicated Tc coordination chemistry. This approach can be extended to numerous studies of Tc systems as this method is one of the most sensitive methods for accurate Tc oxidation state and ligand characterization

3d-4f Resonant Inelastic X-ray Scattering of Actinide Dioxides : Crystal-Field Multiplet Description

A theoretical overview of the core-to-core (3d-4f) resonant inelastic X-ray scattering (RIXS) spectra of actinide dioxides AnO(2) (An = Th, U, Np, Pu, Am, Cu, Bk, Cf) is provided. The 3d-4f RIXS maps were calculated using crystal-field multiplet theory and turned out to be significantly different at the An M-5 vs M-4 edges, because of selection rules and final state effects. The results of the calculations allowed for a general analysis of so-called high-energy-resolution fluorescence-detected X-ray absorption (HERFD-XAS) spectra. The cuts of the calculated RIXS maps along the incident energy axis at the constant emitted energy, corresponding to the maximum of the RIXS intensity, represented the HERFD spectra and provided their comparison with calculated conventional X-ray absorption (XAS) spectra with a reduced corehole lifetime broadening at the An M-5 and M-4 edges. Although the An M-5 HERFD profiles were found to depart from the X-ray absorption cross-section, in terms of appearing additional transitions, the results of calculations for the An M-4 edges demonstrate overall better agreement between the HERFD and XAS spectra for most dioxides, keeping in mind a restricted HERFD resolution, because of the core-hole lifetime broadening in the final state. The results confirm the utility of HERFD for the An chemical state determination and indicate the importance of calculating the entire RIXS process in order to interpret the HERFD data correctly