| AVS 61st International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Monday Sessions |
| Session AC+AS+MI+SA+SS-MoM |
| Session: | Spectroscopy, Microscopy and Dichroism of Actinides and Rare Earths |
| Presenter: | Stefan Minasian, Lawrence Berkeley National Laboratory |
| Authors: | S. Minasian, Lawrence Berkeley National Laboratory E. Batista, Los Alamos National Laboratory C.H. Booth, Lawrence Berkeley National Laboratory D. Clark, Los Alamos National Laboratory J. Keith, Colgate University W. Lukens, Lawrence Berkeley National Laboratory S. Kozimor, Los Alamos National Laboratory R.L. Martin, Los Alamos National Laboratory D. Nordlund, SLAC National Accelerator Laboratory D. Shuh, Lawrence Berkeley National Laboratory T. Tyliszczak, Lawrence Berkeley National Laboratory D. Sokaras, SLAC National Accelerator Laboratory X.-D. Weng, Los Alamos National Laboratory T.-C. Weng, SLAC National Accelerator Laboratory |
| Correspondent: | Click to Email |
The development of a detailed, quantitative understanding of electronic structure and bonding for a broad range actinide materials remains a significant scientific challenge. Recent advances have shown that the 1s to np transition intensities measured by Cl and S K-edge X-ray absorption spectroscopy (XAS) directly relate to coefficients of covalent orbital mixing in M–Cl and M–S bonds. The scientific progress associated with these Cl and S XAS studies suggests that using synchrotron-generated radiation to quantify covalency for ligands beyond Cl and S would have a wide impact. The nature of chemical bonds between actinides and light atoms such as oxygen, nitrogen, and carbon is of particular interest because these interactions control the physics and chemistry of many technologically important processes in nuclear science. However, obtaining accurate light atom K-edge XAS spectra on non-conducting compounds is notoriously difficult, because the measurement is highly sensitive to surface contamination, self-absorption, and saturation effects. Fortunately, recent upgrades at synchrotron facilities, advancements in beamline instrumentation, and sample preparation methods suggest that these insights are now within reach. Specifically, comparing XAS spectra measured in transmission with a scanning transmission X-ray microscope (STXM) with those from non-resonant inelastic X-ray scattering (NIXS) and time-dependent density functional theory provides a sound basis for validation of bulk-like excitation spectra.
Herein, a new effort is discussed that employs these techniques to understand bonding interactions in two well defined series of f-element materials. The actinide sandwich complexes, “actinocenes,” (C8H8)2An (An = Th, Pa, U, Np, Pu) have played a central role in the development of organoactinide chemistry. Results showed two contrasting trends in actinide–carbon orbital mixing, and evidence that covalency does not increase uniformly as the actinide series is traversed. Additionally, the C K-edge XAS spectrum of thorocene represents the first experimental evidence of a ϕ-type orbital interaction. Oxygen K-edge XAS measurements and DFT studies began the lanthanide dioxides LnO2 (Ln = Ce, Pr, Tb), because their electronic structures are well-established from hard X-ray spectroscopies. Preliminary efforts to use lanthanide oxides and lanthanide organometallics as experimental benchmarks for quantitative determinations of covalency in d-block and f-block materials will also be discussed.