title: Structural dynamics of 1,2-diiodoethane in cyclohexane probed by picosecond X-ray liquidography.
abstract: We investigate the structural dynamics of iodine elimination reaction of 1,2-diiodoethane (C(2)H(4)I(2)) in cyclohexane by applying time-resolved X-ray liquidography (TRXL). The TRXL technique combines structural sensitivity of X-ray diffraction and 100 ps time resolution of X-ray pulses from synchrotron and allows direct probing of transient structure of reacting molecules. From the analysis of time-dependent X-ray solution scattering patterns using global fitting based on DFT calculation and MD simulation, we elucidate the kinetics and structure of transient intermediates resulting from photodissociation of C(2)H(4)I(2). In particular, the effect of solvent on the reaction kinetics and pathways is examined by comparison with an earlier TRXL study on the same reaction in methanol. In cyclohexane, the C(2)H(4)I radical intermediate undergoes two branched reaction pathways, formation of C(2)H(4)I-I isomer and direct dissociation into C(2)H(4) and I, while only isomer formation occurs in methanol. Also, the C(2)H(4)I-I isomer has a shorter lifetime in cyclohexane by an order of magnitude than in methanol. The difference in the reaction dynamics in the two solvents is accounted for by the difference in solvent polarity. In addition, we determine that the C(2)H(4)I radical has a bridged structure, not a classical structure, in cyclohexane.
authors: Center for Time-Resolved Diffraction, Department of Chemistry, Graduate School of Nanoscience and Technology (WCU), KAIST, Daejeon, Republic of Korea.
authors: Jeongho
authors: J
authors: Kim
authors: Jae Hyuk
authors: JH
authors: Lee
authors: Joonghan
authors: J
authors: Kim
authors: Sunhong
authors: S
authors: Jun
authors: Kyung Hwan
authors: KH
authors: Kim
authors: Tae Wu
authors: TW
authors: Kim
authors: Michael
authors: M
authors: Wulff
authors: Hyotcherl
authors: H
authors: Ihee
mesh_terms: D002623:Chemistry Techniques, Analytical / Q000295:instrumentation / Q000379:methods*; D003510:Cyclohexanes / Q000737:chemistry*; D006847:Hydrocarbons, Iodinated / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory; D012542:Scattering, Radiation; D017356:Synchrotrons; D013816:Thermodynamics; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: D003510:Cyclohexanes; D006847:Hydrocarbons, Iodinated; C027946:methylene iodide; D000432:Methanol