Visualizing Chemical Reactions in Solution by Picosecond X-Ray Diffraction

We present a time-resolved x-ray diffraction study to monitor the recombination of laser-dissociated iodine molecules dissolved in ${\mathrm{CCl}}_4$. The change in structure of iodine is followed during the whole recombination process. The deexcitation of solute molecules produces a heating of the solvent and induces tiny changes in its structure. The variations in the distance between pairs of chlorine atoms in adjacent ${\mathrm{CCl}}_4$ molecules are probed on the $m\AA$ length scale. However, the most striking outcome of the present work is the experimental determination of temporally varying atom-atom pair distribution functions. Variations of the mean density of the solution during thermal expansion are also followed in real time. One concludes that not only time-resolved optical spectroscopy but also time-resolved x-ray diffraction can be used to monitor atomic motions in liquids. DOI: http://dx.doi.org/10.1103/PhysRevLett.92.125505 © 2004 The American Physical Society