Synchrotron-based x-ray absorption spectroscopy

Studies by Teplyakov et al. provided the experimental evidence for the formation of the Diels-Alder reaction product at the Si(100)-2 x 1 surface [239,240]. A combination of surface-sensitive techniques was applied to make the assignment, including surface infrared (vibrational) spectroscopy, thermal desorption studies, and synchrotron-based X-ray absorption spectroscopy. Vibrational spectroscopy in particular provides a molecular fingerprint and is useful in identifying bonding and structure in the adsorbed molecules. An analysis of the vibrational spectra of adsorbed butadiene on Si(100)-2 x 1 in which several isotopic forms of butadiene (i.e., some of the H atoms were substituted with D atoms) were compared showed that the majority of butadiene molecules formed the Diels-Alder reaction product at the surface. Very good agreement was also found between the experimental vibrational spectra obtained by Teplyakov et al. [239,240] and frequencies calculated for the Diels-Alder surface adduct by Konecny and Doren [237,238]. 

Mineral-liquid or mineral-gas interfaces under reactive conditions cannot be studied easily using standard UHV surface science methods. To overcome the pressure gap between ex situ UHV measurements and the in situ reactivity of surfaces under atmospheric pressure or in contact with a liquid, new approaches are required, some of which have only been introduced in the last 20 years, including scanning tunneling microscopy [28,29], atomic force microscopy [30,31], non-linear optical methods [32,33], synchrotron-based surface scattering [34—38], synchrotron-based X-ray absorption fine structure spectroscopy [39,40], X-ray standing wave... 

It must be emphasized that these marker signals can be used exclusively for the interpretation of Py-FI mass spectra, but not for the interpretation of conventional Cp Py-GC/MS because of the completely different heating and ionization conditions. The interpretation of the routine Py-FI mass spectra will be incrementally improved by the application of complementary techniques such as high-resolution Py-FIMS with a MAT 900 (see below) and synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy (Section 14.3.2). 

Methods of growing importance for speciation and complexation studies of actinides are the synchrotron-based X-ray absorption near-edge structure spectroscopy (XANES) and the extended X-ray absorption fine structure spectroscopy (EXAFS). 

Elemental distribution and chemical state of ppm metal impurities can be measured using synchrotron-based X-ray fluorescence ( iXRF) and X-ray absorption spectroscopy ( iXAS), both with a I -2 irn2 spatial resolution [314]. 

Techniques of microscopic XRF ( j,-XRF) developed in the last 20 years provide 2D images and elemental maps of each element present in the target material. Portable/in situ p-XRF, j,-XRF spectrometers synchrotron-based ( -SRXRF) and micro-x-ray absorption spectroscopy/micro-x-ray absorption near-edge structure spectroscopy (XAS/ J,-XANES) have improved the mineralogical characterization, as well as the elemental and chemical imaging of samples at the submicrometer scale [61]. 

A more recent addition to the diverse array of x-ray based methods is x-ray absorption spectroscopy. In contrast to x-ray diffraction methods which derive their utility from the properties of well defined crystallites, x-ray absorption methods are atomic probes, capable of obtaining both electronic and structural information about a specific type of atom. The growing use of x-ray absorption methods is a result of the greater availability of synchrotron radiation sources which provide the intense broad band x-radiation required. In some instances laboratory based spectrometers utilizing either sealed tubes or rotating anode x-ray generators can also be used. 

The use of synchrotron based in situ x-ray absorption spectroscopy (XAS) for the study of catalysis, both heterogeneous and electrocatalysis has matured over the last decade with simultaneous efforts in the United Sates, European Union and Japan. Some recent exemplification of the state of the art can be obtained in the following references, " and an extensive database of literature on its application to catalysis can be accessed electronically (www.exafs.chem.msu.su/ papers). Detailed aspects on application of the technique and methodology used for data analysis has been recently published. " ... 

The characterization of structure and dynamics in metal carbonyl cluster chemistry has understandably been based around single-crystal X-ray diffraction and NMR spectroscopic studies, respectively. As has been shown in the earlier part of this chapter, these sources of data can be used in conjunction to provide a coherent picture of the possible molecular configurations of a given species and the processes by which they interconvert, at least in favorable cases. In general however, it is not possible to determine the geometric structures of these species in solution, nor to obtain direct experimental evidence to confirm that the same structure(s) obtain in solution as in the solid state. Fortunately the rebirth and exploitation of X-ray absorption spectroscopy (XAS) and in particular the application of synchrotron X-ray sources and improved methods of data analysis to EXAFS (Extended X-ray Absorption Eine Structure) spectroscopy has provided exactly this sort of experimental evidence. In this section we provide selective coverage of such work as relates to the structure and dynamics of metal carbonyl clusters. 

Among the various spectroscopic methods, the most notable one is synchrotron-based X-ray techniques that are revolutionizing soil and environmental chemistry research (Manceau et al, 1992). The most utilized synchrotron-based X-ray technique in soil and environmental chemistry to date has been X-ray absorption spectroscopy. The extended X-ray absorption fine structure spectroscopy (EXAFS) provides specific information on the local environment of the absorber, including coordination number, identity, and distances to nearest and sometimes next nearest neighboring atoms (Fendorff et al, 1994 Schulze and Bertsch, 1995 Fendorff and Sparks, 1996 Bertsch and Hunter, 1998 Sparks,... 

In this chapter we first provide an overview of eommonly applied synchrotron radiation-based X-ray techniques for determining metal speciation in powdered samples, including X-ray absorption spectroscopy, micro X-ray fluorescence, and micro X-ray diffraction (XRD). The seeond part of this ehapter will provide an example of the application of these teehniques to an investigation of lead (Pb) speciation in a house dust sample, characterized by elevated total and bioaccessible Pb concentrations. 

Many combined setups have been developed in the past decades to study catalyst synthesis and reaction processes, many of which employ synchrotron radiation. Perhaps the first example of a successful combination of two techniques is X-ray absorption spectroscopy (XAFS) and diffraction, which was soon followed by the combination of SAXS and WAXS. Other examples in which two techniques have been combined to study systems under reaction include XAFS/FTIR, XRD/Raman, XAFS/UV-Vis, and a number of setups that use non-X-ray based radiation, such as UV-Vis/Raman, FTIR/UV-Vis, NMR/UV-Vis, and EPR/UV-Vis. A number of reports have recently appeared in which the number of combined techniques has been increased to three, including SAXS/WAXS/XAFS, UV-Vis/Raman/XAFS (148), and EPR/UV-Vis/Raman (218), and SAXS/WAXS/XAFS (219). In what follows, we illustrate the power three-in-one in situ spectroscopic methods to unravel chemistry of catalytic solids. 

This book is written by experts from disciplines as diverse as analytical chemistry, nuclear chemistry, environmental science, molecular biology, and medicinal chemistry in order to identify potential hot spots of metallomics and metalloproteomics. The scientific fundamentals of new approaches, like isotopic techniques combined with ICP-MS/ESI-MS/MS, the synchrotron radiation-based techniques. X-ray absorption spectroscopy, X-ray diffraction, and neutron scattering, as well as their various applications, with a focus on mercury, selenium, chromium, arsenic, iron and metal-based medicines are critically reviewed, which can help to understand their impacts on human health. The book will be of particular interest to researchers in the fields of environmental and industrial chemistry, biochemistry, nutrition, toxicology, and medicine. Basically, the book has two aims. The first deals with the educational point of view. Chapters 2 to 7 provide the basic concept of each of the selected nuclear analytical techniques and should be understandable by Master and PhD students in chemistry, physics, biology and nanotechnology. The... 

The task of an X-ray absorption spectrometer is the precise and accurate measurement of the linear X-ray absorption coefficient of a substance. A principal use of such spectrometers is the measurement of X-ray absorption fine structure (XAFS) spectra of solids, liquids, and molecular gases. XAFS consists of modulations in the X-ray absorption coefficient in the vicinity of an X-ray absorption edge, which may extend more than one KeV beyond the edge. Applications and theory of X-ray Absorption Spectroscopy are covered elsewhere in this volume. This article is directed primarily to instrumental requirements for X-ray absorption spectroscopy over the energy range from several KeV X-ray photon energy to approximately 100 KeV, with emphasis on synchrotron radiation based instruments. 

U-XRF spectrometry synchrotron-based micro-x-ray absorption near-edge stmcture spectroscopy multiple collector inductively coupled plasma mass spectrometry... 

In spite of numerous studies on Nd-carboxylate-based catalyst systems a mechanistic understanding of the formation and the chemical structure of the active species is far off. By the application of new analytical methods some progress has recently been achieved. Kwag and co-workers applied synchrotron X-ray absorption in combination with UV-VIS-spectroscopy. These authors succeeded to characterize the reaction product obtained by the pre-formation of the catalyst components NdV HV9/TIBA/DEAC. The following essential features are reported about the reaction product (1) Nd-C bonds (bond length = 1.41 A) with covalent and ionic character, (2) Nd- Cl bonds... 

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