Ultrafast Time‐Resolved Transient Structures of Solids and Liquids by Means of Extended X‐ray Absorption Fine Structure

Abstract

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.

Three-Dimensional Local Structure of Photoexcited Cu Diimine Complex Refined by Quantitative XANES Analysis

“…Forthcoming X-ray free electron lasers will eradicate this obstacle because of its high pulse photon flux and short pulse duration. However, their spectral tunability is limited in comparison with the synchrotron based X-ray sources for spectroscopy studies. – For this reason, XTA employed in currently available synchrotron sources is still suitable for investigating excited-state structures with lifetimes longer than a few hundred picoseconds, as demonstrated in the literature. – XTA’s ability to obtain excited-state electronic and geometric structural information makes it a powerful technique for solving local structures around heavy atoms in disordered media, complementing those acquired from the pump−probe X-ray diffraction for single crystals. – …”

“…[15][16][17] For this reason, XTA employed in currently available synchrotron sources is still suitable for investigating excited-state structures with lifetimes longer than a few hundred picoseconds, as demonstrated in the literature. [18][19][20][21][22][23][24][25][26][27][28] XTA's ability to obtain excited-state electronic and geometric structural information makes it a powerful technique for solving local structures around heavy atoms in disordered media, complementing those acquired from the pump-probe X-ray diffraction for single crystals. [29][30][31] Although, traditionally, interatomic distances have been extracted by analyses of the extended X-ray absorption fine structure (EXAFS), recently developed algorithms allow quantitative determination of bond lengths and angles from X-ray adsorption near edge structure (XANES) spectra.…”