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Published June 2003 | public
Journal Article

Ultrafast Electron Diffraction (UED): A New Development for the 4D Determination of Transient Molecular Structures


With properly timed sequences of ultrafast electron pulses, it is now possible to image complex molecular structures in the four dimensions of space and time with resolutions of 0.01 Å and 1 ps, respectively. The new limits of ultrafast electron diffraction (UED) provide the means for the determination of transient molecular structures, including reactive intermediates and non-equilibrium structures of complex energy landscapes. By freezing structures on the ultrafast timescale, we are able to develop concepts that correlate structure with dynamics. Examples include structure-driven radiationless processes, dynamics-driven reaction stereochemistry, pseudorotary transition-state structures, and non-equilibrium structures exhibiting negative temperature, bifurcation, or selective energy localization in bonds. These successes in the studies of complex molecular systems, even without heavy atoms, and the recent development of a new machine devoted to structures in the condensed phase, establish UED as a powerful method for mapping out temporally changing molecular structures in chemistry, and potentially, in biology. This review highlights the advances made at Caltech, with emphasis on the principles of UED, its evolution through four generations of instrumentation (UED-1 to UED-4) and its diverse applications.

Additional Information

© 2003 Schweizerische Chemische Gesellschaft, Switzerland. Received May 26, 2003. Version of Record online: 10 Jul 2003. We gratefully acknowledge the generous support of the National Science Foundation for building the new generations of UED. Partial support was provided by the Air Force Office of Scientific Research. A. H. Z. and the co-authors (listed below in parentheses) would also like to acknowledge colleagues in our laboratory at Caltech whose contributions over the years have been instrumental in the successful evolution of UED from its infancy to the current state-of-the-art. In chronological order, they are: J. Charles Williamson, Marcos Dantus, Scott B. Kim, Hans Frey, Hyotcherl Ihee, Jianming Cao, Udo M. Gomez, (Vladimir A. Lobastov), (Ramesh Srinivasan), Boyd M. Goodson, (Chong-Yu Ruan), Jonathan S. Feenstra, Franco Vigliotti, Songye Chen, Sang Tae Park, and Shoujun Xu ± the published contributions have been listed in the references.We wish to also thank the late Prof. Verner Schomaker, late Prof. John D. Ewbank, Prof. Hani Elsayed-Ali, and Prof. István Hargittai for sharing with us over the years their experience of electron diffraction; and late Prof. Alexander Prokhorov and Prof. Mikhail Schelev for the collaboration on femtosecond electron sources.

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