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

The emergence of a novel tool of structural chemistry is reviewed; pulsed-electron beam (stroboscopic) gas electron diffraction (GED) synchronous with photoexcitation. About 10 years ago, the first stroboscopic electron diffraction experiments of irradiated gaseous species were performed at Moscow State University, yielding qualitative evidence that intensity changes upon irradiation can be detected in this way. More recently, development of prototype on-line GED data recording techniques at the University of Arkansas allowed for the first successful observations, with quantitatively model-fitted GED signals, of photochemical reactions, i.e. the 193 nm photodissociations of carbon disulfide and of chlorine-substituted ethenes. In addition to summarizing some of 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.