Extended X-ray absorption fine structure

About: Extended X-ray absorption fine structure is a(n) research topic. Over the lifetime, 10452 publication(s) have been published within this topic receiving 276744 citation(s).

Theoretical approaches to x-ray absorption fine structure

Abstract: Dramatic advances in the understanding of x-ray absorption fine structure (XAFS) have been made over the past few decades, which have led ultimately to a highly quantitative theory. This review covers these developments from a unified multiple-scattering viewpoint. The authors focus on extended x-ray absorption fine structure (EXAFS) well above an x-ray edge, and, to a lesser extent, on x-ray absorption near-edge structure (XANES) closer to an edge. The discussion includes both formal considerations, derived from a many-electron formulation, and practical computational methods based on independent-electron models, with many-body effects lumped into various inelastic losses and energy shifts. The main conceptual issues in XAFS theory are identified and their relative importance is assessed; these include the convergence of the multiple-scattering expansion, curved-wave effects, the scattering potential, inelastic losses, self-energy shifts, and vibrations and structural disorder. The advantages and limitations of current computational approaches are addressed, with particular regard to quantitative experimental comparisons.

Multiple-scattering calculations of x-ray-absorption spectra

Abstract: A high-order multiple-scattering (MS) approach to the calculation of polarized x-ray-absorption spectra, which includes both x-ray-absorption fine structure and x-ray-absorption near-edge structure, is presented. Efficient calculations in arbitrary systems are carried out by using a curved-wave MS path formalism that ignores negligible paths, and has an energy-dependent self-energy and MS Debye-Waller factors. Embedded-atom background absorption calculations on an absolute energy scale are included. The theory is illustrated for metallic Cu, Cd, and Pt. For these cases the MS expansion is found to converge to within typical experimental accuracy, both to experiment and to full MS theories (e.g., band structure), by using only a few dozen important paths, which are primarily single-scattering, focusing, linear, and triangular.

X-ray absorption : principles, applications, techniques of EXAFS, SEXAFS, and XANES

Abstract: Theory of EXAFS. Theory of XANES. INSTRUMENTAL AND DATA ANALYSIS. Design of an EXAFS Experiment. EXAFS with Synchrotron Radiation. Laboratory EXAFS Facilities. Data Analysis. APPLICATIONS. Biochemical Application of X-ray Absorption Spectroscopy. Catalysis. Amorphous and Liquid Systems. SEXAFS. XANES Spectroscopy.

Cavity ring‐down optical spectrometer for absorption measurements using pulsed laser sources

Abstract: We have developed a technique which allows optical absorption measurements to be made using a pulsed light source and offers a sensitivity significantly greater than that attained using stabilized continuous light sources. The technique is based upon the measurement of the rate of absorption rather than the magnitude of absorption of a light pulse confined within a closed optical cavity. The decay of the light intensity within the cavity is a simple exponential with loss components due to mirror loss, broadband scatter (Rayleigh, Mie), and molecular absorption. Narrowband absorption spectra are recorded by scanning the output of a pulsed laser (which is injected into the optical cavity) through an absorption resonance. We have demonstrated the sensitivity of this technique by measuring several bands in the very weak forbidden b1Σg−X3Σg transition in gaseous molecular oxygen. Absorption signals of less than 1 part in 106 can be detected.

Interpretation of europium(III) spectra

Abstract: The trivalent europium ion (Eu3+) is well known for its strong luminescence in the red spectral region, but this ion is also interesting from a theoretical point of view. Due to the even number of electrons in the 4f shell (4f6 configuration), the crystal-field perturbation by the crystalline host matrix lifts partly or completely the degeneracies of the 2S+1LJ levels. The Eu3+ ion has the great advantage over other lanthanide ions with an even number of 4f electrons that the starting levels of the transitions in both the absorption and the luminescence spectrum are non-degenerate (J = 0). Moreover, the interpretation of the spectra is facilitated by the small total angular momentum J of the end levels in the transitions. The number of lines observed for the 5D0 → 7FJ transitions in the luminescence spectrum or the 5DJ ← 7F0 transitions in the absorption spectrum allows determining the site symmetry of the Eu3+ ion. This review describes the spectroscopic properties of the trivalent europium ion, with emphasis on the energy level structure, the intensities of the f–f transitions (including the Judd–Ofelt theory), the decay times of the excited states and the use of the Eu3+ ion as a spectroscopic probe for site symmetry determination. It is illustrated how the maximum amount of information can be extracted from optical absorption and luminescence spectra of europium(III) compounds, and how pitfalls in the interpretation of these spectra can be avoided.