Solvent dependent structural perturbations of chemical reaction intermediates visualized by time-resolved x-ray diffraction.
Journal article, 2009

Ultrafast time-resolved wide angle x-ray scattering from chemical reactions in solution has recently emerged as a powerful technique for determining the structural dynamics of transient photochemical species. Here we examine the structural evolution of photoexcited CH(2)I(2) in the nonpolar solvent cyclohexane and draw comparisons with a similar study in the polar solvent methanol. As with earlier spectroscopic studies, our data confirm a common initial reaction pathway in both solvents. After photoexcitation, CH(2)I(2) dissociates to form CH(2)I* + I*. Iodine radicals remaining within the solvent cage recombine with a nascent CH(2)I* radical to form the transient isomer CH(2)I-I, whereas those which escape the solvent cage ultimately combine to form I(2) in cyclohexane. Moreover, the transient isomer has a lifetime approximately 30 times longer in the nonpolar solvent. Of greater chemical significance is the property of time-resolved wide angle x-ray diffraction to accurately determine the structure of the of CH(2)I-I reaction intermediate. Thus we observe that the transient iodine-iodine bond is 0.07 A+/-0.04 A shorter in cyclohexane than in methanol. A longer iodine-iodine bond length for the intermediate arises in methanol due to favorable H-bond interaction with the polar solvent. These findings establish that time-resolved x-ray diffraction has sufficient sensitivity to enable solvent dependent structural perturbations of transient chemical species to be accurately resolved.

Author

J Vincent

Uppsala University

Magnus Andersson

Chalmers, Chemical and Biological Engineering, Molecular Imaging

Mattias Eklund

Uppsala University

Annemarie Wöhri

Chalmers, Chemical and Biological Engineering, Molecular Imaging

Michael Odelius

Stockholm University

Erik Malmerberg

University of Gothenburg

Qingyu Kong

European Synchrotron Radiation Facility (ESRF)

Michael Wulff

European Synchrotron Radiation Facility (ESRF)

Richard Neutze

University of Gothenburg

J Davidsson

Uppsala University

Journal of Chemical Physics

0021-9606 (ISSN) 1089-7690 (eISSN)

Vol. 130 15 154502-

Subject Categories

Chemical Sciences

DOI

10.1063/1.3111401

PubMed

19388754

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3/1/2018 7