High Resolution Crystallographic Studies Using Synchrotron Radiation

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9317770 Coppens In this project in the Physical Chemistry Program of the Chemistry Division, Prof. P. Coppens of the State University of New York at Buffalo will engage in crystallographic research using the National Synchrotron Light Source at the Brookhaven National Laboratory and also perform experiments using advanced conventional facilities. The research consists of several parts: application of anomalous scattering of X-rays to selectively identify site ocupancy, to determine the oxidation states of atoms in solids and to identify spectroscopic transitions; to study the response of crystals to external perturbations, such as laser-induced molecular excitation; and the analysis of modulated and composite solids, which are aperiodic in at least one direction. Very low temperature single crystal techniques are to be used in the analysis of charge densities in crystals, and in the investigation of the temperature-dependence of the structure of low-dimensional conducting solids. Area detectors are to be applied to charge density studies and other fields after new software development aimed at maximizing accuracy of the area-detector intensity data. X-ray diffraction by single crystals has been used for many years to study the structure of organic and inorganic materials. The conventional techniques are based on the use of x-ray tubes, which emit monochromatic radiation of relatively low intensity, thereby limiting their use to large size crystals and strong scatterers. X-radiation emitted by synchrotrons has a continuous range of wavelengths, a low spatial divergence, is polarized, and is much brighter than the radiation emitted from conventional x-ray tubes. These properties allow the determination of the structures of very small crystals, not heretofore possible with conventional techniques, in a much shorter time and with greater accuracy. The new methods are, however, partly still in the development stage. The research to be done in this project i s directed toward improvement of the new technique and the solution of new crystallographic problems in physics and materials science. ***