• EXAFS
  • In addition an analysis technique using the reduced chi(2) goodness of fit between FEFF EXAFS simulations and the experimental transient absorption signal in energy space has been successfully tested as a function of excited state population and chemical shift, demonstrating its applicability in situations where the fractional excited state population cannot be determined through other measurements. (epfl.ch)
  • In the high kinetic energy range of the photoelectron the scattering cross-section with neighbor atoms is weak and the absorption spectra are dominated by EXAFS (Extended X-ray Absorption Fine Structure) where the scattering of the ejected photoelectron of neighboring atoms can be approximated by single scattering events. (wikipedia.org)
  • Extended X-ray absorption fine structure (EXAFS) refers to the oscillatory variation of the X-ray absorption as a function of photon energy beyond an absorption edge. (springer.com)
  • For atoms either in a molecule or embedded in a condensed phase, the variation of absorption coefficient at energies above the absorption edge displays a complex fine structure called EXAFS. (springer.com)
  • Later in his career, Freeman developed an interest in the applications of EXAFS spectroscopy to metalloprotein structure, collaborating with both James Penner-Hahn and Keith Hodgson. (wikipedia.org)
  • spectra
  • We investigate the sensitivity of X-ray absorption spectra, simulated using a general method, to properties of molecular excited states. (epfl.ch)
  • We demonstrate that, at the ADC(2)x level of theory, ground state X-ray absorption spectra may be accurately reproduced, validating the method. (epfl.ch)
  • Significantly, the calculated X-ray absorption spectra of the excited states are found to be sensitive to both geometric distortions (structural dynamics) and the electronic character (electronic dynamics) of the initial state, suggesting that core excitation spectroscopies will be useful probes of excited state non-adiabatic dynamics. (epfl.ch)
  • The XAS spectra of condensed matter are usually divided in three energy regions: The edge region usually extends in a range of few eV around the absorption edge. (wikipedia.org)
  • The distinction is critical because in spectroscopy final states are more susceptible to many-body effects than initial states, meaning that NEXAFS spectra are more easily calculable than photoemission spectra. (wikipedia.org)
  • Soft x-ray absorption spectra are usually measured either through the fluorescent yield, in which emitted photons are monitored, or total electron yield, in which the sample is connected to ground through an ammeter and the neutralization current is monitored. (wikipedia.org)
  • Comparison of the specimen's spectrum with the spectra of samples of known composition produces quantitative results (after some mathematical corrections for absorption, fluorescence and atomic number). (wikipedia.org)
  • there are two main techniques for analysis of spectra of characteristic X-ray radiation: energy-dispersive X-ray spectroscopy (EDS) and wavelength dispersive X-ray spectroscopy (WDS). (wikipedia.org)
  • atoms
  • For isolated atoms, the absorption coefficient decreases monotonically as a function of energy beyond the edge. (springer.com)
  • In transmission experiments, generally drops off monotonically due primarily to the energy dependence of the ionization chamber efficiency and the absorption due to other atoms. (springer.com)
  • Atoms can be excited by a high-energy beam of charged particles such as electrons (in an electron microscope for example), protons (see PIXE) or a beam of X-rays (see X-ray fluorescence, or XRF). (wikipedia.org)
  • threshold
  • Beyond the role of the unoccupied density of states and matrix elements in single electron excitations, many-body effects appear as an "infrared singularity" at the absorption threshold in metals. (wikipedia.org)
  • resonant
  • Relativistic Lorentz contraction bumps the frequency by another factor of γ {\displaystyle \gamma } , thus multiplying the gigahertz frequency of the resonant cavity that accelerates the electrons into the X-ray range. (wikipedia.org)
  • The angle dependence of the x-ray absorption tracks the orientation of resonant bonds due to dipole selection rules. (wikipedia.org)
  • peaks
  • When the x-ray photon energy resonantly connects a core level with a narrow final state in a solid, such as an exciton, readily identifiable characteristic peaks will appear in the spectrum. (wikipedia.org)
  • measurements
  • We report time-resolved X-ray absorption measurements after photolysis of carbonmonoxy myoglobin performed at the LCLS X-ray free electron laser with nearly 100 fs (FWHM) time resolution. (osti.gov)
  • structural
  • The introduction of pump-probe techniques to the field of x-ray absorption spectroscopy (XAS) has allowed the monitoring of both structural and electronic dynamics of disordered systems in the condensed phase with unprecedented accuracy, both in time and in space. (epfl.ch)
  • electrons
  • The cathode ray tube or an x-ray tube was the method used to pass electrons through a crystal of numerous elements. (wikipedia.org)
  • fluorescence
  • In fluorescence experiments, on the other hand, the baseline rises as a function of energy owing to increasing sample penetration, increased Compton scattering, reduced absorption of the scattering, and other effects. (springer.com)
  • energy
  • Above the IP the absorption cross section attenuates gradually with the X-ray energy. (wikipedia.org)
  • For instance, in the ultra soft X-ray region (below about 1 keV), crystal field excitations give rise to the energy loss. (wikipedia.org)
  • type
  • X-ray absorption spectroscopy (XAS) is ideal in this respect because it is chemically selective and can be implemented in any type of medium. (epfl.ch)
  • XAS is a type of absorption spectroscopy from a core initial state with a well defined symmetry therefore the quantum mechanical selection rules select the symmetry of the final states in the continuum which usually are mixture of multiple components. (wikipedia.org)
  • Scanning transmission X-ray microscopy (STXM) is a type of X-ray microscopy in which a zone plate focuses an X-ray beam onto a small spot, a sample is scanned in the focal plane of the zone plate and the transmitted X-ray intensity is recorded as a function of the sample position. (wikipedia.org)
  • Study
  • We performed a comparative study of the soft x-ray absorption spectroscopy of the LiMn2O4 and Li1.15Mn1.85O4 electrode materials with a quantitative analysis of the Mn oxidation states. (osti.gov)
  • molecular
  • For many years the edge region was referred to as the "Kossel structure" but now it is known as "absorption edge region" since the Kossel structure refers only to unoccupied molecular final states which is a correct description only for few particular cases: molecules and strongly disordered systems. (wikipedia.org)
  • atom
  • Though simply defined as x = ( µ - µ o )/ µ o (where μ and µ o are the observed and 'free atom' absorption coefficients, respectively), the determination of x (generally termed as 'background substration') is by no means straightforward since µ o is generally not known. (springer.com)
  • techniques
  • Although the advantages of using grazing incidence (GI) techniques in X-ray scattering and spectroscopy have been known for a long time (Yoneda and Horiuchi 1971), the use of such geometry has only been developed fully with the advent of highly collimated X-ray sources, particularly synchrotrons. (geoscienceworld.org)
  • beams
  • Unfortunately, in the area of x-ray beams, several terms mean exactly the same thing as brilliance. (wikipedia.org)
  • sources
  • When comparing x-ray sources, an important measure of quality of the source is called brilliance. (wikipedia.org)
  • Intensity means power density per unit of area, but for x-ray sources, usually means brilliance. (wikipedia.org)