X-ray Absorption and Scattering

In conclusion it must be said that little new insight on the effects of ions on the water structure has been gained by the XAS results. Most of these having been 

3 Effects of Ions on Water Stnicture and Vice Versa 

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Berrodier, I., Farges, F., Benedetti, M., Winterer, M., Brown Jr, G. E., Deveughele, M. (2004). Adsorption mechanisms of trivalent gold on iron- and aluminum-(oxy)hydroxides. Part 1 X-ray absorption and Raman scattering spectroscopic studies of Au(III) adsorbed on ferrihydrite, goethite, and boehmite. Geochimica et Cosmochimica Acta, 68(14), 3019-3042. doi 10.1016/j.gca.2004.02.009... 

In bulk samples, X-ray yields need to be adjusted by the so-called "ZAF" correction. Z stands for the element number (heavier elements reduce the electron beam intensity more than lighter elements, because they are more efficient back-scatterers), A for absorption (different elements have different cross sections for X-ray absorption), and F for secondary fluorescence (the effect described above). Corrections are much less important when the sample is a film with a thickness of 1 pm or less, because secondary effects are largely reduced. The detection limit is set by the accuracy with which a signal can be distinguished from the bremsstrahlung background. In practice, this corresponds to about 100 ppm for elements heavier than Mg. 

In extreme cases a multiple-scattering, sharp resonant structure can result in which the electron is in a quasi-bound state (155). One example is the white line, which is among the most spectacular features in X-ray absorption and is seen in spectra of covalently bonded materials as sharp ( 2eV wide) peaks in absorption immediately above threshold (i.e., the near continuum). The cause of white lines has qualitatively been understood as being due to a high density of final states or due to exciton effects (56, 203). Their description depends upon the physical approach to the problem for example, the LiUii white lines of the transition metals are interpreted as a density-of-states effect in band-structure calculations but as a matrix-element effect in scattering language. 

The electronic structure of tetrahedral oxyanions and their derivatives has been extensively studied by many authors during the past decades. The earlier attempts were summarized by Prins [1]. Since the work of Walsh [2] and that of Wolfsberg and Helmholz [3] several semi-empirical theoretical studies have been published [4-7]. Later ab initio [8-10] and scattered wave calculations [11] have been also reported. Among the experimental investigations, Prins mentioned the electron spin resonance measurements of radicals formed by ejection or addition of an electron from or to certain oxyanions, obtaining information on just those molecular orbitals which contained unpaired electrons. [12] X-ray absorption and emission studies provided usefial information on a limited number of molecular orbitals in the valence band [13-19]... 

Physical methods for size determination are mainly related to the use of X-ray based diffraction, scattering and absorption techniques, microscopy, and magnetic measurements. Physical and chemical methods may be combined, for example, in the use of infrared spectroscopy coupled to the use of probe molecules such as CO to determine the fraction of exposed metal atoms. However, as Chp 3 has already dealt with characterisation of supported metal systems by X-ray absorption and infrared spectroscopies in some detail, they will not be included here. 

See also Microscopy Techniques Atomic Force and Scanning Tunneiing Microscopy. Surface Ana-iysis X-Ray Photoeiectron Spectroscopy Auger Eiec-tron Spectroscopy ion Scattering. X-Ray Absorption and Diffraction X-Ray Absorption. X-Ray Fiuorescence and Emission X-Ray Diffraction - Singie Crystai. 

In areas of characterization of composite films, a multitude of methods have been used to understand their fundamental physical and chemical properties. Table 1 and studies on layered films suggest that some of the more common methods to characterize inorganic composite films are FTIR, Raman, surface methods, QCM, AFM, cychc voltammetry, and other electrochemical methods. As other methods become more common, those hke X-ray absorption and neutron scattering will be used to study the nature of the interfaces between the components of the... 

The experimental papers cover the various spectroscopic techniques and a few deal with special materials. The introductory chapter (62) by Baer and Schneider presents an overview of this field and helps tie the various aspects together that are reviewed in detail in the remaining chapters of the volume. Photoemission studies (UPS - ultraviolet photoemission spectroscopy, and XPS - X-ray photoemission spectroscopy) on various materials are discussed by Campagna and Hillebrecht (chapter 63)- intermetallic compounds, by Lynch and Weaver (chapter 66)— cerium and its compounds, and by Hiifner (chapter 67) - chalcogenides. Other experimental techniques covered include BIS (bremsstrahlung isochromat spectroscopy) by Hillebrecht and Campagna (chapter 70), X-ray absorption and X-ray emission by Rohler (chapter 71) and inelastic electron scattering by Netzer and Matthew (chapter 72). 

The techniques such as jff-particle and y-ray absorption and scattering and radioisotope X-ray fluorescence methods, all of which can provide information about the chemical nature of the sample, will be considered to be physical... 

Water-molecule dimers are proposed to be the main, low-energy, component of liquid water. The molecular distances under interaction of two polarized dimers are presented in Fig.la and in Supplementary Tablel. This molecular structure is consistent with measurements of X-ray and neutron scattering [17], and with recent reports of X-ray absorption and emission spectroscopy, revealing proton delocalization [18], strong electron sharing [19] and double, rather than tetrahedral. 

Further particle size measurement techniques are light scattering, cascade impaction, X-ray absorption and fluorescence, permeability, and adsorption. The last two are discussed further in the next section. 

The remainder of this section is concerned firstly with a brief outline of the classical description of X-ray scattering by electrons and of how this scattering leads to the production of X-ray diffraction patterns. The second part presents a description of X-ray absorption and in particular of absorption fine structure. 

Almost every modem spectroscopic approach can be used to study matter at high pressures. Early experiments include NMR [ ], ESR [ ] vibrational infrared [33] and Raman [ ] electronic absorption, reflection and emission [23, 24 and 25, 70] x-ray absorption [Tf] and scattering [72], Mossbauer [73] and gems analysis of products recovered from high-pressure photochemical reactions [74]. The literature contains too many studies to do justice to these fields by describing particular examples in detail, and only some general mles, appropriate to many situations, are given. 

Rehr J J, Albers R C and Zabinski S I 1992 High order multiple scattering calculation of x-ray absorption fine structure Phys. Rev. Lett. 69 3397-400... 

Colorimetry, in which a sample absorbs visible light, is one example of a spectroscopic method of analysis. At the end of the nineteenth century, spectroscopy was limited to the absorption, emission, and scattering of visible, ultraviolet, and infrared electromagnetic radiation. During the twentieth century, spectroscopy has been extended to include other forms of electromagnetic radiation (photon spectroscopy), such as X-rays, microwaves, and radio waves, as well as energetic particles (particle spectroscopy), such as electrons and ions. ... 

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