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Originally published in Science Express on 14 July 2005
Science 19 August 2005:
Vol. 309. no. 5738, pp. 1223 - 1227
DOI: 10.1126/science.1114782
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Reports

Ultrafast X-ray Diffraction of Transient Molecular Structures in Solution

H. Ihee,1* M. Lorenc,2 T. K. Kim,1 Q. Y. Kong,2 M. Cammarata,2,3 J. H. Lee,1 S. Bratos,4 M. Wulff2

We report direct structural evidence of the bridged radical (CH2ICH2·) in a polar solution, obtained using time-resolved liquid-phase x-ray diffraction. This transient intermediate has long been hypothesized to explain stereo-chemical control in many association and/or dissociation reactions involving haloalkanes. Ultrashort optical pulses were used to dissociate an iodine atom from the haloethane molecule (C2H4I2) dissolved in methanol, and the diffraction of picosecond x-ray pulses from a synchrotron supports the following structural dynamics, with ~0.01 angstrom spatial resolution and ~100 picosecond time resolution: The loss of one iodine atom from C2H4I2 leads to the C-I-C triangular geometry of CH2ICH2·. This transient C2H4I then binds to an iodine atom to form a new species, the C2H4I-I isomer, which eventually decays into C2H4 + I2. Solvent dynamics were also extracted from the data, revealing a change in the solvent cage geometry, heating, and thermal expansion.

1 Department of Chemistry and School of Molecular Science (BK21), Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 305-701, Republic of Korea.
2 European Synchrotron Radiation Facility, Grenoble Cedex 38043, Boîte Postal 220, France.
3 National Institute for the Physics of Matter and Department of Physical and Astronomical Sciences, via Archirafi 36, 90123, Palermo, Italy.
4 Laboratoire de Physique Théorique des Liquides, Université Pierre et Marie Curie, Case courrier 121, 4, Place Jussieu, Paris Cedex 75252, France.

* To whom correspondence should be addressed. E-mail: hyotcherl.ihee{at}kaist.ac.kr

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Imaging Atomic Structure and Dynamics with Ultrafast X-ray Scattering.
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Spatiotemporal reaction kinetics of an ultrafast photoreaction pathway visualized by time-resolved liquid x-ray diffraction.
T. K. Kim, M. Lorenc, J. H. Lee, M. Lo Russo, J. Kim, M. Cammarata, Q. Kong, S. Noel, A. Plech, M. Wulff, et al. (2006)
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