Studies By Means Of Synchrotron Radiation

Extended X-ray Absorption Fine Structure [EXAFS) has become known inrecent years as a technique for studying the environment of specific elementsin chemical systems. This has been related to the advent of synchrotronradiation. The significance of the present studies is to find out how tocalculate the EXAFS spectra of our samples, otherwise called "model compounds"(standards or calibrants) viz:potassium bromide - KBr;manganese( II) ammonium sulphate hexahydrate - MnSOJNH ) SO .6H O;and strontium bromide hexahydrate - SrBr2.6H O;from the information available to us from their crystal structures. The EXAFSdata for the samples were obtained from the Daresbury Synchrotron RadiationSource and analysed via appropriate UMIST computer programmes. We haveassumed that the scattering factors from the Daresbury MUFPOT programmeas used in our calculations in the EXAFS region beyond - 70 eV are reliable.The first objective of the work involved carrying out calculations in the EXAFSregime termed "short-range" refinements for convenience.The second objective investigated the possibility of extending these calculationsto the inner region called XANES (X-ray Absorption Near Edge Structure).Although these calculations gave a fit in the EXAFS region, the f i t in theinner region was not satisfactory. The final objective was to attempt tomodify the scattering factors in the XANES regime and termed "long-range"refinements. The computer programme involved employed curve f i t t i ng byLeast Squares, and Fourier transformation techniques. The attempts to modifythe scattering factors in the XANES region were largely successful and theresults obtained from these studies will be of use in refinements determiningunknown structures of compounds with similar atoms to those in the presentinvestigation.

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