Structural and vibrational kinetics of photoexcitation processes using time resolved electron diffraction

This paper describes the historical background and current status of structural and vibrational kinetic studies of photoexcitation processes using pulsed beam gas electron diffraction. The development of time resolved electron diffraction (TRED) required essential changes in the traditional experimental and theoretical procedures of gas electron diffraction. On the experimental side, over the last decade or so, research at the University of Arkansas has led to construction of a prototype on-line data recording system that, combined with a laser-driven pulsed photocathode, enables time-resolved investigations spanning the time domain from microseconds to picoseconds. On the theoretical side, new techniques allow one to model TRED data in terms of a molecule's potential energy surface or, alternatively, to apply stochastic procedures to solve the inverse problem, i.e. to determine the PES from the diffraction data. The importance of considering appropriate vibrational properties is demonstrated. Diverse aspects of TRED modeling of dissociation and pre-dissociation processes are described, including formalisms based on wave packet dynamics, spatial anisotropy, chaotic nuclear dynamics, Wigner distribution functions, tomographic reconstruction, and coherently excited molecular ensembles. (C) 2000 Elsevier Science B.V. All rights reserved.