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Covalent An-Cl bonding in series of +4 actinide hexachlorides, AnCl6 2-(An IV = U, Th, Np, Pu) have been characterized using Cl K-edge XAS and DFT. The results suggest that the 6d-orbital mixing is more substantial than that of the 5f-orbital. Additionally, the results indicate that 5fcovalent bonding with the Cl 3p orbitals is more substantial for Pu than for Th, U, and Np.

We report the development of a laboratory-based Rowland-circle monochromator that incorporates a low power x-ray (bremsstrahlung) tube source, a spherically-bent crystal analyzer (SBCA), and an energy-resolving solid-state detector. This relatively inexpensive, introductory level instrument achieves 1-eV energy resolution for photon energies of ~5 keV to ~10 keV while also demonstrating a net efficiency previously seen only in laboratory monochromators having much coarser energy resolution. Despite the use of only a compact, air-cooled 10 W xray tube, we find count rates for nonresonant x-ray emission spectroscopy (XES) comparable to those achieved at monochromatized spectroscopy beamlines at synchrotron light sources. For xray absorption near edge structure (XANES), the monochromatized flux is small (due to the use of a low-powered x-ray generator) but still useful for routine transmission-mode studies of concentrated samples. These results indicate that upgrading to a standard commercial highpower line-focused x-ray tube or rotating anode x-ray generator would result in monochromatized fluxes of order 10 6 -10 7 photons/s with no loss in energy resolution. This work establishes core technical capabilities for a rejuvenation of laboratory-based hard x-ray spectroscopies that could have special relevance for contemporary research on catalytic or electrical energy storage systems using transition-metal, lanthanide or noble-metal active species.

Self-assembled monolayers (SAMs) of dipolar phosphonic acids can tailor the interface between organic semiconductors and transparent conductive oxides. When used in optoelectronic devices such as organic light emitting diodes and solar cells, these SAMs can increase current density and photovoltaic performance. The molecular ordering and conformation adopted by the SAMs determine properties such as work function and wettability at these critical interfaces. We combine angle-dependent near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) to determine the molecular orientations of a model phenylphosphonic acid on indium zinc oxide, and correlate the resulting values with density functional theory (DFT). We find that the SAMs are surprisingly well-oriented, with the phenyl ring adopting a well-defined tilt angle of 12-16° from the surface normal. We find quantitative agreement between the two experimental techniques and density functional theory calculations. These results not only provide a detailed picture of the molecular structure of a technologically important class of SAMs, but also resolve a long-standing ambiguity regarding the vibrational-mode assignments for phosphonic acids on oxide surfaces, thus improving the utility of PM-IRRAS for future studies.

Synthetic efforts to prepare indium phosphide (InP) quantum dots (QDs) have historically generated emissive materials with lower than unity quantum yields. This property has been attributed to structural and electronic defects associated with the InP core as well as the chemistry of the shell materials used to overcoat and passivate the InP surface. Consequently, the uniformity of the core-shell interface plays a critical role. Using X-ray emission spectroscopy (XES) performed with a recently developed benchtop spectrometer, we studied the evolution of oxidized phosphorus species arising across a series of common, but chemically distinct, synthetic methods for InP QD particle growth and subsequent ZnE (E = S or Se) shell deposition. XES afforded us the ability to measure the speciation of phosphorus reliably, quantitatively, and more efficiently (with respect to both the quantity of material required and the speed of the measurement) than with traditional techniques, i.e., X-ray photoelectron spectroscopy and magic angle spinning solid state nuclear magnetic resonance spectroscopy. Our findings indicate that even with deliberate care to prevent phosphorus oxidation during InP core synthesis, typical shelling approaches unintentionally introduce oxidative defects at the core-shell interface, limiting the attainable photoluminescence quantum yields. Disciplines

X-ray absorption spectroscopy using fluorescence and transmission (via a scanning transmission X-ray microscope), and linear-response density functional theory. The results suggest that moving from Group 6 to Group 7 or down the triads increases M-O e* (π*) mixing. Meanwhile, t 2 * mixing (σ* + π*) remains relatively constant within the same Group. These unexpected changes in frontier orbital energy and composition are evaluated in terms of periodic trends in d orbital energy and radial extension. 3Introduction.The nature of chemical bonds between metals and light atoms such as oxygen, nitrogen, and carbon is of widespread interest because these interactions control the physics and chemistry of many technologically important processes and compounds. Light atoms are prone to form highly covalent metalligand multiple bonds involving one σ bond and one or more π bonds, resulting in oxo, imido, nitrido, alkylidene, alkylidyne, and carbido functionalities with many desirable chemical reactivities and physical properties. 1 Among this diverse group, metal oxides stand out because of their widespread presence in biological and bio-inspired processes and for applications utilizing their unique magnetic, electronic, and thermal properties. [2][3][4][5][6][7][8][9][10][11][12][13] Developing a clear understanding of how M-O electronic structure and orbital mixing changes for a range of metal oxo compounds and materials will greatly benefit attempts to advance these technologies.Among approaches explored previously, ligand K-edge X-ray absorption spectroscopy (XAS) has emerged as an effective method for quantitatively probing electronic structure and orbital mixing in metal-chlorine and metal-sulfur bonds. 14 This spectroscopic technique probes bound state transitions between core ligand 1s orbitals and unoccupied molecular orbitals. The excitations can only have transition intensity if the empty acceptor orbitals contain ligand p character. 14 At first glance, such an approach seems well-suited for studying metal-oxygen bonding. However, attempts to use this technique to study non-conducting molecular systems are complicated by experimental barriers derived from the low energy of the oxygen K-edge (ca. 530 eV), which magnifies issues associated with surface contamination, saturation, and self-absorption effects.In this manuscript, we overcome these challenges and evaluate relative changes in metal-oxo electronic structure and orbital mixing for non-conducting molecular solids using O K-edge spectroscopy in conjunction with hybrid density functional theory (DFT) calculations. Specifically, non-resonant inelastic X-ray scattering (NIXS), XAS, and linear-response density functional theory (TDDFT) are used as Density functional theory calculations using relativistic effective core potentials (RECPs) were conducted to determine how antibonding molecular orbital compositions and energies varied as (1) metals 5 changed within a group (Cr, Mo, W and Mn, Tc, Re) and (2) metal charges increased from M 6+ (Group 6) to M 7+ (Group 7)...

Momentum-transfer (q) dependent non-resonant inelastic x-ray scattering measurements were made at the N 4,5 edges for several rare earth compounds. With increasing q, giant dipole resonances diminish, to be replaced by strong multiplet lines at lower energy transfer. These multiplets result from two different orders of multipole scattering and are distinct for systems with simple 4f 0 and 4f 1 initial states. A many-body theoretical treatment of the multiplets agrees well with the experimental data on ionic La and Ce phosphate reference compounds. Comparing measurements on CeO 2 and CeRh 3 to the theory and the phosphates indicates sensitivity to hybridization as observed by a broadening of 4f 0 -related multiplet features. We expect such strong, nondipole features to be generic for NIXS from f-electron systems.

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