Ultrafast time-resolved transient structures of solids and liquids by means of extended X-ray absorption fine structure.

Detection of ultrafast transient structures and the evolution of ultrafast structural intermediates during the course of reactions has been a long standing goal of chemists and biologists. This article will be restricted to nanosecond, picosecond and shorter time-resolved extended X-ray absorption fine structure (EXAFS) studies, its aim being to present the progress and problems encounter in measurements and understanding the structure of transients. The recent advances in source technology has stimulated a wide variety of novel experiments using both synchrotrons and smaller laboratory size systems. With more efficient X-ray lenses and detectors many of the previously difficult experiments to perform, because of the exposure time required and weak signals, will now be easily performed. The experimental system for the detection of ultrafast, time-resolved EXAFS spectra of molecules in liquids is described and the method for the analysis of EXAFS spectra to yield transient structures is given. We believe that utilizing our table-top ultrafast X-ray source and the polycapillary optics in conjunction with dispersive spectrometer and charge coupled devices (CCD) we will be able to determine the structure of many reaction intermediates and excited states of chemical and biological molecules in solid and liquid state.