Synchrotron-based x-ray absorption

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). 

Brown GE Jr, Parks GA (1989) Synchrotron-based X-ray absorption studies of cation enviromnents in Earth materials. Rev Geophys 27 519-533... 

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]. 

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,... 

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]. 

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

Synchrotron-based N K-edge X-ray absorption near-edge fine structure (XANES)... 

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... 

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. 

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