THE STROBOSCOPIC GAS ELECTRON-DIFFRACTION METHOD FOR INVESTIGATION OFTIME-RESOLVED STRUCTURAL KINETICS IN PHOTOEXCITATION PROCESSES

The emergence of a novel tool of structural chemistry is reviewed; pul sed-electron beam (stroboscopic) gas electron diffraction (GED) synchr onous with photoexcitation. About 10 years ago, the first stroboscopic electron diffraction experiments of irradiated gaseous species were p erformed at Moscow State University, yielding qualitative evidence tha t intensity changes upon irradiation can be detected in this way. More recently, development of prototype on-line GED data recording techniq ues at the University of Arkansas allowed for the first successful obs ervations, with quantitatively model-fitted GED signals, of photochemi cal reactions, i.e. the 193 nm photodissociations of carbon disulfide and of chlorine-substituted ethenes. In addition to summarizing some o f the current structural work, the paper describes the characteristic aspects of pulsed-beam GED, the requisite on-line data recording, and non-conventional data analysis techniques capable of interpreting GED signals from non-equilibrium ensembles in arbitrary vibrational states .