Extended X-ray absorption fine structure

About: Extended X-ray absorption fine structure is a research topic. Over the lifetime, 10452 publications have been published within this topic receiving 276744 citations.

Core–Shell Structure of Palladium Hydride Nanoparticles Revealed by Combined X-ray Absorption Spectroscopy and X-ray Diffraction

Abstract: We report an in situ, temperature and H2 pressure-dependent, characterization of (2.6 ± 0.4) nm palladium nanoparticles supported on active carbon during the process of hydride phase formation. For the first time the core–shell structure is highlighted in the single-component particles on the basis of a different atomic structure and electronic configurations in the inner “core” and surface “shell” regions. The atomic structure of these particles is examined by combined X-ray powder diffraction (XRPD), which is sensitive to the crystalline core region of the nanoparticles, and by first shell analysis of extended X-ray absorption fine structure (EXAFS) spectra, which reflects the averaged structure of both the core and the more disordered shell. In the whole temperature range (0–85 °C), XRPD analysis confirms the existence of two well-separated α- and β-hydride phases with the characteristic flat plateau in the phase transition region of the pressure-lattice parameter isotherms. In contrast, first shell in...

Metal-assisted hydroformylation on a SiO2-attached rhodium dimer. In situ EXAFS and FT-IR observations of the dynamic behaviors of the dimer site

Abstract: trans-(Rh(C{sub 5}Me{sub 5})(CH{sub 3})){sub 2}({mu}-CH{sub 2}){sub 2} was supported on the SiO{sub 2} surface by the reaction with OH groups of SiO{sub 2} at 313 K, followed by evacuation at 373 K. In this attaching reaction, the Rh dimer complexes were bound to the SiO{sub 2} surface through Rh-O(surface) bonds, losing one CH{sub 3} ligand and one C{sub 5}Me{sub 5} ligand per Rh dimer. The attached Rh dimers were found to be more active and selective than a conventionally prepared Rh/SiO{sub 2} catalyst. The structure change of the Rh dimer sites in each reaction step for catalytic hydroformylation was followed by means of in-situ FT-IR and in situ EXAFS techniques. The Rh-Rh bond in the attached Rh dimers (Rh-Rh = 0.262 nm) was cleaved by CO adsorption to form monomer pairs (Rh(C{sub 2}H{sub 5})(CO){sub 2}(O-Si) + Rh(C{sub 5}Me{sub 5})(O-Si)). Heating the monomer pairs to 423 K under vacuum resulted in CO insertion, with new peaks exhibited at 1,710 and 1,394 cm{sup {minus}1} due to the acyl ligand.

High overtones of C–H stretch in liquid benzene measured by laser optoacoustic spectroscopy

Abstract: We present a first measurement of the absorption profile of the eighth harmonic of the C–H stretch in liquid benzene using a recently developed optoacoustic absorption measurement technique involving a pulsed dye laser and submersed piezoelectric transducer. The absorption maximum occurs at 21 040±7cm−1, with a peak absorption coefficient of (9.2±1.5) ×10−5 cm−1. The full linewidth of the absorption profile is 354±9cm−1. We have previously reported similar measurements for the sixth and seventh harmonics. We have also obtained spectra of lower harmonics by conventional spectrophotometry. We make a comparative survey of the studies of this series of overtone absorptions. With our accurate determination of the nth harmonic absorption for large n, we propose an improved anharmonic formula to fit the experimental peak positions. We also note that the absorption linewidth increases linearly with n in liquid benzene.

f-f origin of the insulating state in uranium dioxide: X-ray absorption experiments and first-principles calculations

Abstract: We have performed x-ray absorption experiments on uranium dioxide (UO${}_{2}$) at the O $1s$, U $4d$, U $4f$, and U $5d$ edges. After comprehensive energy calibrations for O $1s$, U $4d$, and U $4f$ spectra, we have used the U $4d$ and $4f$ spectra to sort the energetic positions of the $5f$ and the $6d$ states in the unoccupied band unambiguously. This demonstrates conclusively that UO${}_{2}$ is an $f$-$f$ Mott-Hubbard insulator, where the electronic repulsion between $f$ electrons is responsible for the insulating state. Calculations performed within the U-corrected generalized gradient approximation of the optical response of UO${}_{2}$ permit direct comparison with the absorption spectra and confirm the experimental results.

X-ray absorption and magnetic circular dichroism characterizations of Mn doped ZnO

Abstract: We report the near-edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) experiments on well characterized Mn doped ZnO thin films that show ferromagnetism at room temperature. The NEXAFS measurements at O K edge clearly exhibit a preedge spectral feature which evolves with Mn doping, similar to one observed in hole-doped cuprates and manganites. The Mn L3,2 edge NEXAFS spectra exhibit divalent Mn apart from mixed valent Mn3+∕Mn4+ states. The spectral features of XMCD at Mn L3,2 edge demonstrate that ferromagnetism comes from Mn2+ ions and its dichroism shape is independent of Mn concentration.