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Published February 14, 2002 | public
Journal Article

Ultrafast Electron Diffraction and Structural Dynamics: Transient Intermediates in the Elimination Reaction of C_2F_4I_2


We give a full account of our earlier report on the structural dynamics in the elimination reaction of C_2F_4I_2, as studied with the newly constructed third-generation apparatus for ultrafast electron diffraction (UED3) at Caltech (Ihee, H.; Lobastov, V. A.; Gomez, U., Goodson B. M.; Srinivasan, R.; Ruan, C.-Y.; Zewail, A. H. Science 2000, 291, 458). Improvements in experimental stability, sensitivity, resolution, and versatility provided by UED3 permitted the reaction to be probed with spatial and temporal resolution of ∼1 ps and ∼0.01 Å, respectively, and with a sensitivity to chemical change of ∼1%. In addition to the improvements in apparatus design, a number of advancements in data processing, analysis, and modeling were developed which are described here in detail for the first time. With UED, we directly observed the prompt (within 5 ps) formation of the C_2F_4I transient structure, and its subsequent decay with a rate of (25 ± 7 ps)^(-1). The molecular structure of the C_2F_4I radical was determined to be classical, not bridged-and was refined via a least-squares fitting procedure. These experimental results are compared with recent predictions obtained from ab initio and density functional theory calculations (Ihee, H.; Kua, J.; Goddard, W. A.; Zewail A. H. J. Phys. Chem. A 2001, 105, 3623), yielding quantitative agreement to within 0.03 Å between the experimental and theoretical structures for the transient intermediate.

Additional Information

© 2002 American Chemical Society. Received: November 12, 2001; In Final Form: February 25, 2002. Publication Date (Web): April 2, 2002. This work was supported by the National Science Foundation and the Air Force Office of Scientific Research. We gratefully acknowledge U. Gomez for his work in the primary construction of the UED3 apparatus. We also thank C.-Y. Ruan and D. Zhong for helpful discussions.

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