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Solvent dependent structural perturbations of chemical reaction intermediates visualized by time-resolved x-ray diffraction
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
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2009 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, no 15, 154502- p.Article 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 center dot+I center dot. Iodine radicals remaining within the solvent cage recombine with a nascent CH2I center dot radical to form the transient isomer CH2I-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 CH2I-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.

Place, publisher, year, edition, pages
2009. Vol. 130, no 15, 154502- p.
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
Chemical Sciences
URN: urn:nbn:se:uu:diva-129090DOI: 10.1063/1.3111401ISI: 000265486300028OAI: oai:DiVA.org:uu-129090DiVA: diva2:337564
Available from: 2010-08-06 Created: 2010-08-05 Last updated: 2010-08-06Bibliographically approved

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