Solvent dependent structural perturbations of chemical reaction intermediates visualized by time-resolved x-ray diffraction

Journal Article · Tue Apr 21 00:00:00 EDT 2009 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.3111401· OSTI ID:21559696

Vincent, Jonathan; Eklund, Mattias; Davidsson, Jan ^[1]; Andersson, Magnus; Woehri, Annemarie B ^[2]; Odelius, Michael ^[3]; Malmerberg, Erik; Neutze, Richard ^[4]; Kong, Qingyu; Wulff, Michael ^[5]

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1. Department of Photochemistry and Molecular Science, Uppsala University, P.O. Box 523, S-751 20 Uppsala (Sweden)
2. Department of Chemical and Biological Engineering, Chalmers University of Technology, P.O. Box 462, S-405 30 Gothenburg (Sweden)
3. FYSIKUM, Stockholm University, Albanova, S-106 91 Stockholm (Sweden)
4. Department of Chemistry, Biochemistry and Biophysics, Gothenburg University, P.O. Box 462, S-405 30 Gothenburg (Sweden)
5. European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble (France)

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{sub 2}I{sub 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{sub 2}I{sub 2} dissociates to form CH{sub 2}I{center_dot}+I{center_dot}. Iodine radicals remaining within the solvent cage recombine with a nascent CH{sub 2}I{center_dot} radical to form the transient isomer CH{sub 2}I-I, whereas those which escape the solvent cage ultimately combine to form I{sub 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{sub 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.

• OSTI ID: 21559696
• Journal Information: Journal of Chemical Physics, Vol. 130, Issue 15; Other Information: DOI: 10.1063/1.3111401; (c) 2009 American Institute of Physics; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BOND LENGTHS
COMPARATIVE EVALUATIONS
CYCLOHEXANE
DISSOCIATION
DISTURBANCES
INTERACTIONS
IODINE
ISOMERS
LIQUIDS
METHANOL
PHOTOCHEMISTRY
PHOTOLYSIS
RADICALS
REACTION INTERMEDIATES
SENSITIVITY
SOLUTIONS
SOLVENTS
TIME RESOLUTION
TRANSIENTS
X-RAY DIFFRACTION
ALCOHOLS
ALKANES
CHEMICAL REACTIONS
CHEMISTRY
COHERENT SCATTERING
CYCLOALKANES
DECOMPOSITION
DIFFRACTION
DIMENSIONS
DISPERSIONS
ELEMENTS
EVALUATION
FLUIDS
HALOGENS
HOMOGENEOUS MIXTURES
HYDROCARBONS
HYDROXY COMPOUNDS
LENGTH
MIXTURES
NONMETALS
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
RESOLUTION
SCATTERING
TIMING PROPERTIES