X Ray Spectroscopy

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R. Mewe - One of the best experts on this subject based on the ideXlab platform.

  • Stellar Coronal X-Ray Spectroscopy
    Physics of Solar and Stellar Coronae: G.S. Vaiana Memorial Symposium, 1993
    Co-Authors: R. Mewe
    Abstract:

    Since the Solar corona was detected as an X-Ray source, X-Ray Spectroscopy has proven to be an invaluable tool in studying the tenuous hot (1–10 MK) coronae surrounding the Sun and many other stars throughout a large part of the HR diagram, with the probable eXception of single very cool giant and supergiant stars. This paper reviews our present observational knowledge of stellar X-Ray Spectroscopy, focussing on the understanding of the structure of the coronae around cool solar-type stars, as has emerged from the medium-resolution spectral X-Ray observations carried out with the EINSTEIN and EXOSAT observatories. We show some eXamples of differential emission measure modelling for simulated spectra to be observed by the spectrometer on board the recently launched EXtreme Ultraviolet EXplorer (EWE). Finally, we consider the perspectives offered by high-resolution dispersive Spectroscopy with future missions like NASA’s Advanced X-Ray Astrophysics Facility AXAF and ESA’s X-Ray Multi-Mirror Mission XMM and the eXpected performance of non-dispersive Spectroscopy with superconductor technology currently in development. A few spectral simulations are given to demonstrate the diagnostic capabilities.

  • X-Ray Spectroscopy of stellar coronae
    The Astronomy and Astrophysics Review, 1991
    Co-Authors: R. Mewe
    Abstract:

    From the early discovery in 1948 of X-Rays from the Solar corona, X-Ray Spectroscopy has proven to be an invaluable tool in studying hot astrophysical and laboratory plasmas. Because the emission line spectra and continua from optically thin plasmas are fairly well known, high-resolution X-Ray Spectroscopy has its most obvious application in the measurement of optically thin sources such as the coronae of stars. In particular X-Ray observations with theEINSTEIN observatory have demonstrated that soft X-Ray emitting coronae are a common feature among stars on the cool side of the Hertzsprung-Russell diagram, with the probable eXception of single very cool giant and supergiant stars and A-type dwarfs. Observations with the spectrometers aboardEINSTEIN andEXOSAT have shown that data of even modest spectral resolution (α/Δα = 10–100) permit the identification of coronal material at different temperatures whose eXistence may relate to a range of possible magnetic loop structures in the hot outer atmospheres of these stars. The higher spectral resolution of the neXt generation of spectrometers aboard NASA'sAXAF and ESA'sXMM will allow to fully resolve the coronal temperature structure and to enable velocity diagnostics and the determination of coronal densities, from which the loop geometry (i.e. surface filling factors and loop lengths) can be derived. In this paper various diagnostic techniques are reviewed and the spectral results fromEINSTEIN andEXOSAT are discussed. A number of spectral simulations forAXAF andXMM, especially high-resolution iron K-shell, L-shell, and2s-2p spectra in the wavelength regions around 1.9 A, 10 A, and 100 A, respectively, are shown to demonstrate the capabilities for temperature, density, and velocity diagnostics. Finally, iron K-shell spectra are simulated for various types of detectors such as microcalorimeter, Nb-junction, and CCD.

Vittal K. Yachandra - One of the best experts on this subject based on the ideXlab platform.

  • Calcium in the oXygen-evolving compleX: structural and mechanistic role determined by X-Ray Spectroscopy.
    Journal of photochemistry and photobiology. B Biology, 2011
    Co-Authors: Vittal K. Yachandra, Junko Yano
    Abstract:

    This review describes the results from X-Ray Absorption Spectroscopy studies that have contributed to an understanding of the role of Ca in the photosynthetic water-oXidation reaction. The results include the first Mn, Ca and Sr X-Ray Spectroscopy studies using Ca or Sr-substituted PS II samples that established the presence of a MnCa heteronuclear structure and its orientation, and the most recent Sr X-Ray Spectroscopy study using biosynthetically prepared Sr-containing PS II in the various S-states that provide important insights into the requirement for Ca in the mechanism of the Mn(4)Ca catalytic center.

  • X-Ray Spectroscopy-based structure of the Mn cluster and mechanism of photosynthetic oXygen evolution
    Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2001
    Co-Authors: J H Robblee, R M Cinco, Vittal K. Yachandra
    Abstract:

    AbstractThe mechanism by which the Mn-containing oXygen evolving compleX (OEC) produces oXygen from water has been of great interest for over 40 years. This review focuses on how X-Ray Spectroscopy has provided important information about the structure of this Mn compleX and its intermediates, or S-states, in the water oXidation cycle. X-Ray absorption near-edge structure Spectroscopy and high-resolution Mn Kβ X-Ray emission Spectroscopy eXperiments have identified the oXidation states of the Mn in the OEC in each of the intermediate S-states, while eXtended X-Ray absorption fine structure eXperiments have shown that 2.7 Å Mn–Mn di-μ-oXo and 3.3 Å Mn–Mn mono-μ-oXo motifs are present in the OEC. X-Ray Spectroscopy has also been used to probe the two essential cofactors in the OEC, Ca2+ and Cl−, and has shown that Ca2+ is an integral component of the OEC and is proXimal to Mn. In addition, dichroism studies on oriented PS II membranes have provided angular information about the Mn–Mn and Mn–Ca vectors. Based on these X-Ray Spectroscopy data, refined models for the structure of the OEC and a mechanism for oXygen evolution by the OEC are presented

L J Allen - One of the best experts on this subject based on the ideXlab platform.

  • quantitative elemental mapping at atomic resolution using X Ray Spectroscopy
    Physical Review Letters, 2014
    Co-Authors: Gerald Kothleitner, M J Neish, Nathan R Lugg, S D Findlay, Werner Grogger, Ferdinand Hofer, L J Allen
    Abstract:

    Elemental mapping using energy-dispersive X-Ray Spectroscopy in scanning transmission electron microscopy, a well-established technique for precision elemental concentration analysis at submicron resolution, was first demonstrated at atomic resolution in 2010. However, to date atomic resolution elemental maps have only been interpreted qualitatively because the elastic and thermal scattering of the electron probe confounds quantitative analysis. Accounting for this scattering, we present absolute scale quantitative comparisons between eXperiment and quantum mechanical calculations for both energy dispersive X-Ray and electron energy-loss Spectroscopy using off-aXis reference measurements. The relative merits of removing the scattering effects from the eXperimental data against comparison with direct simulations are eXplored.

  • atomic resolution chemical mapping using energy dispersive X Ray Spectroscopy
    Physical Review B, 2010
    Co-Authors: A J Dalfonso, B Freitag, D O Klenov, L J Allen
    Abstract:

    We demonstrate atomic-resolution chemical mapping using energy-dispersive X-Ray Spectroscopy in scanning transmission electron microscopy. Theoretical simulations of the imaging process demonstrate that these images are directly interpretable. This is due to the fact that the effective ionization interaction is local and this is an incoherent mode of imaging.

J H Robblee - One of the best experts on this subject based on the ideXlab platform.

  • X-Ray Spectroscopy-based structure of the Mn cluster and mechanism of photosynthetic oXygen evolution.
    Biochimica et biophysica acta, 2001
    Co-Authors: J H Robblee, R M Cinco, V K Yachandra
    Abstract:

    The mechanism by which the Mn-containing oXygen evolving compleX (OEC) produces oXygen from water has been of great interest for over 40 years. This review focuses on how X-Ray Spectroscopy has provided important information about the structure of this Mn compleX and its intermediates, or S-states, in the water oXidation cycle. X-Ray absorption near-edge structure Spectroscopy and high-resolution Mn Kbeta X-Ray emission Spectroscopy eXperiments have identified the oXidation states of the Mn in the OEC in each of the intermediate S-states, while eXtended X-Ray absorption fine structure eXperiments have shown that 2.7 A Mn-Mn di-mu-oXo and 3.3 A Mn-Mn mono-mu-oXo motifs are present in the OEC. X-Ray Spectroscopy has also been used to probe the two essential cofactors in the OEC, Ca2+ and Cl-, and has shown that Ca2+ is an integral component of the OEC and is proXimal to Mn. In addition, dichroism studies on oriented PS II membranes have provided angular information about the Mn-Mn and Mn-Ca vectors. Based on these X-Ray Spectroscopy data, refined models for the structure of the OEC and a mechanism for oXygen evolution by the OEC are presented.

  • X-Ray Spectroscopy-based structure of the Mn cluster and mechanism of photosynthetic oXygen evolution
    Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2001
    Co-Authors: J H Robblee, R M Cinco, Vittal K. Yachandra
    Abstract:

    AbstractThe mechanism by which the Mn-containing oXygen evolving compleX (OEC) produces oXygen from water has been of great interest for over 40 years. This review focuses on how X-Ray Spectroscopy has provided important information about the structure of this Mn compleX and its intermediates, or S-states, in the water oXidation cycle. X-Ray absorption near-edge structure Spectroscopy and high-resolution Mn Kβ X-Ray emission Spectroscopy eXperiments have identified the oXidation states of the Mn in the OEC in each of the intermediate S-states, while eXtended X-Ray absorption fine structure eXperiments have shown that 2.7 Å Mn–Mn di-μ-oXo and 3.3 Å Mn–Mn mono-μ-oXo motifs are present in the OEC. X-Ray Spectroscopy has also been used to probe the two essential cofactors in the OEC, Ca2+ and Cl−, and has shown that Ca2+ is an integral component of the OEC and is proXimal to Mn. In addition, dichroism studies on oriented PS II membranes have provided angular information about the Mn–Mn and Mn–Ca vectors. Based on these X-Ray Spectroscopy data, refined models for the structure of the OEC and a mechanism for oXygen evolution by the OEC are presented

Oliver Kuhn - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical X-Ray Spectroscopy of Transition Metal Compounds
    arXiv: Chemical Physics, 2018
    Co-Authors: Sergey I Bokarev, Oliver Kuhn
    Abstract:

    X-Ray Spectroscopy is one of the most powerful tools to access structure and properties of matter in different states of aggregation as it allows to trace atomic and molecular energy levels in course of various physical and chemical processes. X-Ray spectroscopic techniques probe the local electronic structure of a particular atom in its environment, in contrast to UV/Vis Spectroscopy, where transitions generally occur between delocalized molecular orbitals. Complementary information is provided by using a combination of different absorption, emission, scattering as well as photo- and autoionization X-Ray methods. However, interpretation of the compleX eXperimental spectra and verification of eXperimental hypotheses is a non-trivial task and powerful first principles theoretical approaches that allow for a systematic investigation of a broad class of systems are needed. Focussing on transition metal compounds, L-edge spectra are of particular relevance as they probe the frontier d-orbitals involved in metal-ligand bonding. Here, near-degeneracy effects in combination with spin-orbit coupling lead to a complicated multiplet energy level structure, which poses a serious challenge to quantum chemical methods. MCSCF theory has been shown to be capable of providing a rather detailed understanding of eXperimental X-Ray Spectroscopy. However, it cannot be considered as a 'blackboX' tool and its application requires not only a command of formal theoretical aspects, but also a broad knowledge of already eXisting applications. Both aspects are covered in this overview.

  • a time correlation function approach to nuclear dynamical effects in X Ray Spectroscopy
    Journal of Chemical Physics, 2017
    Co-Authors: Sven Karsten, Sergey I Bokarev, Sergei D Ivanov, Saadullah G. Aziz, Oliver Kuhn
    Abstract:

    Modern X-Ray Spectroscopy has proven itself as a robust tool for probing the electronic structure of atoms in compleX environments. Despite working on energy scales that are much larger than those corresponding to nuclear motions, taking nuclear dynamics and the associated nuclear correlations into account may be of importance for X-Ray Spectroscopy. Recently, we have developed an efficient protocol to account for nuclear dynamics in X-Ray absorption and resonant inelastic X-Ray scattering spectra [Karsten et al., J. Phys. Chem. Lett. 8, 992 (2017)], based on ground state molecular dynamics accompanied with state-of-the-art calculations of electronic eXcitation energies and transition dipoles. Here, we present an alternative derivation of the formalism and elaborate on the developed simulation protocol using gas phase and bulk water as eXamples. The specific spectroscopic features stemming from the nuclear motions are analyzed and traced down to the dynamics of electronic energy gaps and transition dipole...