title: Ultrafast x-ray diffraction of transient molecular structures in solution.
abstract: 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 approximately 0.01 angstrom spatial resolution and approximately 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.
authors: Department of Chemistry and School of Molecular Science (BK21), Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 305-701, Republic of Korea. hyotcherl.ihee@kaist.ac.kr
authors: H
authors: H
authors: Ihee
authors: M
authors: M
authors: Lorenc
authors: T K
authors: TK
authors: Kim
authors: Q Y
authors: QY
authors: Kong
authors: M
authors: M
authors: Cammarata
authors: J H
authors: JH
authors: Lee
authors: S
authors: S
authors: Bratos
authors: M
authors: M
authors: Wulff
mesh_terms: D003198:Computer Simulation; D005609:Free Radicals; D006847:Hydrocarbons, Iodinated / Q000737:chemistry*; D007536:Isomerism; D000432:Methanol / Q000737:chemistry; D015394:Molecular Structure; D012542:Scattering, Radiation; D012996:Solutions; D012997:Solvents / Q000737:chemistry; D017356:Synchrotrons; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors; D014961:X-Ray Diffraction / Q000379:methods*; D014965:X-Rays
chemical_list: D005609:Free Radicals; D006847:Hydrocarbons, Iodinated; D012996:Solutions; D012997:Solvents; C027946:methylene iodide; D000432:Methanol