Solvent dependent structural perturbations of chemical reaction intermediates visualized by time-resolved x-ray diffraction.
Artikel i vetenskaplig tidskrift, 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.


J Vincent

Uppsala universitet

Magnus Andersson

Chalmers, Kemi- och bioteknik, Molekylär mikroskopi

Mattias Eklund

Uppsala universitet

Annemarie Wöhri

Chalmers, Kemi- och bioteknik, Molekylär mikroskopi

Michael Odelius

Stockholms universitet

Erik Malmerberg

Göteborgs universitet

Qingyu Kong

European Synchrotron Radiation Facility (ESRF)

Michael Wulff

European Synchrotron Radiation Facility (ESRF)

Richard Neutze

Göteborgs universitet

J Davidsson

Uppsala universitet

Journal of Chemical Physics

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

Vol. 130 154502-