Large Angle X-Ray Scattering LAXS

This method provides unvaluable informations on the short and medium range order in disordered atomic architectures amorphous solids, glasses but also liquids or complexes in solution. The fast development and the economical importance of 

In order to have accurate informations from the radial distribution function (RDF), it is necessary to have a good counting statistics and to extend the measurement as far as possible in the k space (k = 4ji sin 0/A). This leads of course to time-consuming data collections. The improvement of linear detector permits to shorten the collection time anyhow, with a classical X-ray tube and Mo Ka wavelength, the data collection takes a few hours to go up to 17 A. The synchrotron beam allows faster experiments and the possibility to work in the hard X-ray part of the spectrum extending considerably the k region available. A realistic possibility for the future ESRF machine seems to be k , = 100 (2). 

The first peak, at 2.30 A, can be assigned as the Au—S vector. The major peak 2 corresponds to a second neighbour distance of 3.35 A and a gold—gold interaction. This Au—Au distance leads to an Au—S—Au angle equal to 94°. The third major peak 3, at 5.8 A, corresponds to the next Au...Au interaction. Assuming the 

S—Au—S angle equal to 180°, the chain conformation depends only on the torsional 

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A detailed investigation of the structure of amorphous PcRu by large-angle X-ray scattering (LAXS)269 showed that in the solid state dimeric species exist with a Ru-Ru distance in the magnitude of a double bond. Current experiments using the extended X-ray absorption fine structure (EXAFS) method confirm these results.279... 

A second piece of indirect evidence relating the 30 ppm peak in aluminosilicates to Al rather than Al species comes from large angle X-ray scattering (LAXS) experiments on aluminosilicate glasses (Schmiicker et al. 1999). The aluminium site occupancies of a number of glass compositions were determined from their Al NMR spectra and used to calculate the pair distribution function (PDF) profile which was... 

The structure of the bis(triphenylphosphine)gold(I) complex (193) in pyridine solution was examined by large angle X-ray scattering (LAXS). The bond distances (Au—P 0.2325 nm and Au to the six closest C atoms 0.344 nm) were in agreement with those found for the solid state complex. No coordination of Au with pyridine was observed260. 

Despite numerous investigations of Grignard compounds, almost no information exists about inlra- and interatomic distances of these reagents in solution. This is not necessarily remarkable, since the methods of physical chemistry discussed in the previous section are of course not able lo provide such information. But X-ray absorption spectroscopy (EXAFS) and large angle X-ray scattering (LAXS) can. 

A recent QMCF MD and LAXS (large angle X-ray scattering) study [76] of the sulfate ion has once more demonstrated the reliability of this simulation technique for the description of composite solutes and an accuracy equivalent to best experimental methods. Precise predictions of vibrational spectra as well as the solvation energy of this anion [77] have clearly indicated the ability of the QMCF MD approach to investigate a variety of properties in a general and comprehensive way. 

This means, for example, the study of the three dimensional order on very small single crystals, phase transitions or transformations under physical or chemical factors of crystalline powders but also vitreous transition of glasses, large angle and small angle X-ray scattering (LAXS—SAXS) of amorphous phases, liquids or coordination complexes in solution. 

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