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.

Picosecond X-ray Absorption Spectroscopy of a Photoinduced Iron(II) Spin Crossover Reaction in Solution

Abstract: In this study, we perform steady-state and time-resolved X-ray absorption spectroscopy (XAS) on the iron K-edge of [Fe(tren(py)3)](PF6)2 dissolved in acetonitrile solution. Static XAS measurements on the low-spin parent compound and its high-spin analogue, [Fe(tren(6-Me-py)3)](PF6)2, reveal distinct spectroscopic signatures for the two spin states in the X-ray absorption near-edge structure (XANES) and in the X-ray absorption fine structure (EXAFS). For the time-resolved studies, 100 fs, 400 nm pump pulses initiate a charge-transfer transition in the low-spin complex. The subsequent electronic and geometric changes associated with the formation of the high-spin excited state are probed with 70 ps, 7.1 keV, tunable X-ray pulses derived from the Advanced Light Source (ALS). Modeling of the transient XAS data reveals that the average iron−nitrogen (Fe−N) bond is lengthened by 0.21 ± 0.03 A in the high-spin excited state relative to the ground state within 70 ps. This structural modification causes a change i...

Transition strengths in the visible–infrared absorption spectrum of I2

Abstract: The contributions of the 1Πu←X, B←X, and A←X transitions to the absorption coefficient of I2 in the 4200–8000 A region are reassessed in light of recent results concerning the 1Πu and A potentials and their diffuse absorption spectra. Earlier estimates of the continuum underlying the B←X discrete spectrum are augmented by additional high‐resolution ’’between‐the‐lines’’ absorption measurements, corrected for residual B–X absorption using the very reliable spectroscopic constants now available for this system. The 1Πu–X and A–X systems are now estimated to be about 10% weaker than in the previous analysis [J. Tellinghuisen J. Chem. Phys. 58, 2821 (1973)]. For the region 2.6–2.8 A sampled in absorption, the estimates of the B–X transition strength ‖μe‖2 remain close to the previous values.

Simultaneous measurement of the two-photon coefficient and free-carrier cross section above the bandgap of crystalline silicon

Abstract: We report what is to our knowledge the first simultaneous measurement of the two-photon absorption coefficient and the free-carrier cross section above the bandgap in a semiconductor. This is also the first observation of two-photon absorption of 1 μm radiation in single-crystal Si at room temperature in a regime where a two-photon stepwise process involving indirect absorption followed by free-carrier absorption is usually dominant. A critical pulsewidth (and fluence) is established below (and above) which two-photon absorption cannot be neglected. Pulses that range from 4 to 100 ps in duration are then used to isolate the irradiance-dependent two-photon absorption from the fluence-dependent free-carrier absorption. We obtain an indirect two-photon absorption coefficient of 1.5 cm/GW and extract a free-carrier cross section of 5 \times 10^{-18} cm2by using a simple technique that does not require a knowledge of the actual carrier density.

Recent advances in x-ray absorption spectroscopy

Abstract: Using x-ray absorption spectroscopy recent progress is achieved all over in solid state physics. This review focuses on these advances, with particular emphasis on applications to surface physics and to magnetism of ultrathin 3d and 5d films that are made possible by the use of undulators in third generation synchrotron radiation sources: the unambiguous appearance of an atomic extended x-ray absorption fine structure for atomic adsorbates and of σ* resonances in near-edge x-ray absorption fine structure spectra of oriented molecules is demonstrated. The induced magnetism at the interfaces of 3d and 5d layers is studied by x-ray magnetic circular dichroism. Fundamental aspects of the spectroscopy are clarified for rare earth crystals. The determination of the ground state properties and the detailed understanding of the underlying mechanisms was obtained by comparison of the experimental data to state-of-the-art ab initio calculations.

Metallic Pd Nanoparticles Formed by Pd−O−Ce Interaction: A Reason for Sintering-Induced Activation for CO Oxidation

Abstract: Ambient-temperature CO oxidation activity of Pd/CeO2 was found to increase by more than 20 times after thermal aging at 900 °C in air. Although the aging resulted in a significant sintering accompanied by a 92% loss of surface area from 92 to 7 m2·g−1, Pd metal dispersion was preserved at a high value (0.57). The analysis using transmission electron microscopy (TEM), high-angle annular dark-field (HAADF)-scanning transmission electron microscopy (STEM), extended X-ray absorption fine structure (EXAFS), and X-ray photoelectron spectroscopy (XPS) demonstrated that the activation is driven by metal−support interactions followed by phase transformation. Owing to the formation of Pd−O−Ce bonding at the PdO/CeO2 interface, Pd oxide species are highly dispersed into the surface structure of CeO2. The Pd oxide becomes unstable when the temperature reaches ≥800 °C, where thermodynamic PdO/Pd phase equilibrium is reached. Finally, the Pd−O−Ce surface moiety is fragmented into metallic Pd particles with a size of 1 ...