| Research Abstract |
The use of the extended X-ray absorption fine structure (EXAFS) in the field of coordination chemistry has rapidly expanded in recent years. EXAFS refers to the oscillatory variation of the X-ray absorption as a function of photon energy beyond an X-ray absorption edge and provides structural information about the local environment at the periphery of the X-ray absorbing atoms. To attain a sufficient signal to noise ratio, high intensity radiation source is required; synchrotron orbital radiation (SOR) is suitable for measurements of EXAFS spectrum. However, the effective use of SOR is as yet very limited mainly due to the availability of the beamtime, spatial restriction, and insufficient developing of the germinative investigations. Thus, from this standpoint, various types of laboratory EXAFS apparatuses have been designed and improved.
On the other hand, no attempt for the application of the laboratory EXAFS system to the fast time-resolved X-ray absorption spectroscopy has been car
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ried out so far. We constructed the time-resolved laboratory EXAFS system and reported its applications to the fast redox reaction between aqua Fe(III) ion and thiosulfate ion in aqueous solution. The time-resolved laboratory EXAFS system consists of four parts; (1) a commercially available X-ray source (Philips PW1729 X-ray generator), (2) an LiF(200) flat diffracton crystal (2d = 4.027 A^^ﾟ, Philips PW1530/30) as an X-ray detector, and (4) a newly designed stopped-flow apparatus for X-ray absorption measurements with a slit-type mixing chamber. This apparatus allowa us to measure the fast time-resolved (-several seconds) X-ray absorption spectra accompanying the electron transfer reactions in solution between aqua Fe(III) ion and thiosulfate ion. In future, time-resolved X-ray absorption spectra measured by our laboratory EXAFS system, when fully interpreted, would provide much more direct information on the coordination number, geometry, effective charge, and degree of covalency as for the identity of the reaction intermediate in the electron transfer reaction in solutions. Less
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