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ReportsUltrafast X-ray Diffraction of Transient Molecular Structures in Solution
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
1 Department of Chemistry and School of Molecular Science (BK21), Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 305-701, Republic of Korea. 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.
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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Science. ISSN 0036-8075 (print), 1095-9203 (online)