Ions, absorption, detection structures

The surface extended X-ray absorption fine structure (SEXAFS) method can use either an electron or an ion detection signal (Koningsberger and Prins, 1988). The classification of analytical techniques may be considered in terms of incident and emitted radiation, resolution, and sensitivity, according to Table 4.7, which lists eight of the many possible techniques (Briggs and Seah, 1990 Buckley, 1981 Watts, 1990). Many of the surface analysis techniques were introduced into many laboratories over the years of 1968 to 1970. This resulted from the maturing of clean vacuum systems which could achieve pressures, down to 10"8 Pa. At these low pressures, it is possible to obtain and maintain atomically clean surfaces. 

Munoz-Paez et al. [114] performed extended X-ray absorption fine structure studies on aqueous solutions of Cr and Zn +. They detected second coordination shells in both cases with coordination numbers of 13.3 + 1 (Cr +) and 11.6 + 1.5 (Zn ). The same group performed Monte Carlo [115] and molecular dynamic [116, 117] simulations of [Cr(H20)6] " in dilute aqueous solutions using an ab initio Cr + hydrate-water interaction potential. They found second shell coordination numbers of 14 from both simulations. Furthermore, from simulations and EXAFS measurements they concluded that chloride ions are situated beyond the second hydration shell. 

The X-ray absorption spectroscopy (XAS) methods provide information about the electronic and structural properties of matter. Thus, X-ray absorption nearedge spectroscopy (XANES) is adequate for the observation of local electronic and geometric structures of elements, while extended X-ray absorption fine structure (EXAFS) provides information concerning the coordination environment of metals, metal ions, and nonmetals. To improve time resolution and spectral quahty, sophisticated techniques such as EDXAFS (energy-dispersive X-ray absorption fine structure spectroscopy) and HERFD XAS (high-energy resolution fluorescence detection X-ray absorption spectroscopy) have been developed. All mentioned X-ray methods have a common requirement for high-briUiance X-ray sources such as available at a synchrotron. 

An unknown X shows a hroad absorption band in the infrared at 3200-3550 cm but none in the 1620-1780 cm region. It contains only C, H, and O. A 116-mg sample was treated with an excess of methylmagnesium bromide, producing 48.7 mL of methane gas collected over mercury at 20 °C and 750 mm Hg. The mass sp>ectrum ofXhas its molecular ion (barely detectable) at 116 w/zand a fragment peak at 98. What does this information tell you about the structure of X ... 

As NRA is sensitive only to the nuclei present in the sample, it does not provide information on chemical bonding or microscopic structure. Hence, it is often used in conjunction with other techniques that do provide such information, such as ESCA, optical absorption. Auger, or electron microscopy. As NRA is used to detect mainly light nuclei, it complements another accelerator-based ion-beam technique, Rutherford backscattering (RBS), which is more sensitive to heavy nuclei than to light nuclei. 

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