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Solvent dependent structural perturbations of chemical reaction intermediates visualized by time-resolved x-ray diffraction
Uppsala Univ, Dept Photochem & Mol Sci.
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2009 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, no 15Article in journal (Refereed) Published
Abstract [en]

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 CH2I2 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, CH2I2 dissociates to form CH2I⋅+I⋅. Iodine radicals remaining within the solvent cage recombine with a nascent CH2I⋅ radical to form the transient isomer CH2I−I, whereas those which escape the solvent cage ultimately combine to form I2 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 CH2I−I reaction intermediate. Thus we observe that the transient iodine-iodine bond is 0.07 ű0.04 Å 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.

Place, publisher, year, edition, pages
2009. Vol. 130, no 15
Keyword [en]
free radical reactions, hydrogen bonds, iodine, liquid structure, organic compounds, perturbation theory, photochemistry, photodissociation, photoexcitation, photolysis, solvent effects, spectrochemical analysis, time resolved spectra, X-ray diffraction
National Category
Computer and Information Science
URN: urn:nbn:se:kth:diva-75452DOI: 10.1063/1.3111401ISI: 000265486300028OAI: diva2:490497
QC 20120207Available from: 2012-02-05 Created: 2012-02-05 Last updated: 2012-02-07Bibliographically approved

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Vincent, Jonathan
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