Ultrafast chemical kinetics: Elementary chemical act

Predictions of the classical theory of chemical reaction rates are compared with experimental results obtained by ultrafast time-resolved X-ray diffraction techniques. Our analysis is illustrated with the reaction I + I = I2 in solution at times immediately preceding recombination. Main features of experimentally detected dynamics are discussed and are compared with what is expected according to Eyring and Kramers. It is emphasized that atomic dynamics are unexpectedly complex at very earliest times.