Filming atomic motions in liquids

Basic techniques in ultrafast time-resolved optical spectroscopy and x-ray diffraction are described for a broad scientific community. Basic experimental setups are presented, and theories for the interpretation of experimental data are briefly described. The power of these ultrafast techniques is shown with a few selected examples. It is shown in particular how they permit to film atomic motions during a chemical reaction. The strong and weak points of the two complementary techniques are discussed in some detail. A number of basic references are included to help interested readers. Future developments of ultrafast techniques are conjectured at the end of the paper.