Spatiotemporal reaction kinetics of an ultrafast photoreaction pathway visualized by time-resolved liquid x-ray diffraction
- Tae Kyu Kim†,
- Maciej Lorenc‡,§,
- Jae Hyuk Lee†,
- Manuela Lo Russo‡,
- Joonghan Kim†,
- Marco Cammarata‡,¶,
- Qingyu Kong‡,
- Sylvie Noel‡,
- Anton Plech‖,
- Michael Wulff‡,††, and
- Hyotcherl Ihee†,‡‡
- †Department of Chemistry and School of Molecular Science (BK21), Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, South Korea;
- ‡European Synchrotron Radiation Facility, Grenoble Cedex 9, France;
- ¶National Institute for the Physics of Matter and Department of Physical and Astronomical Sciences, University of Palermo, via Archirafi 36, 90123 Palermo, Italy; and
- ‖Fachbereich Physik der Universität Konstanz, Universitätsstrasse 10, D-78457 Konstanz, Germany
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Edited by Peter M. Rentzepis, University of California, Irvine, CA, and approved May 9, 2006 (received for review March 10, 2006)
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Fig. 1.Schematic diagram for reaction channels and energies in photodissociation of HgI2 in solution. (A) Putative reaction channels after photodissociation of HgI2 in solution. (B) Relative energies of the dissociation products of HgI2 in solution. All values were calculated by density functional theory.
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Fig. 2.TRXD signal as a function of time delay for HgI2 in methanol. (A) Raw difference images on the detector for selected time delays. (B) Difference–diffraction intensities, qΔS(q), excited minus nonexcited. Shown are radial averages of the 2D images from A. Error bars represent the experimental error associated with each scattering angle. (C) Difference RDFs, rΔS(r). Shown are sine-Fourier transforms of the difference intensities in B.
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Fig. 3.Spatiotemporal reaction kinetics determined by TRXD. (A) The population changes of the various molecular species as a function of time delay after photodissociation of HgI2 in methanol. (B) The change in the solvent density (red) and temperature (blue), where the baseline stems from the geminate ultrafast reaction pathway. Note the duality between the decay in excited-state population and the rise in temperature. (C) A schematic reaction mechanism determined by TRXD in solution.
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Fig. 4.Contributions from the solute-only, solute–solvent (cage), and solvent–solvent correlations to the difference intensities and the difference RDFs for HgI2 in methanol. The curve fitting is based on MD and experimental solvent differentials and includes intramolecular and intermolecular contributions from the solutes and the solvent. The experimental (black, with experimental errors) and theoretical (red) difference intensity (A) and difference RDFs (B) at 100 ps are shown. Also shown are the decomposed components: solute without cage (orange), cage effects (blue), and solvent contribution (green). Decomposed components of cage effects (blue) and solvent contribution (green) in B are multiplied by a factor of 3 to magnify major peaks and valleys. The assignments of the main components for the major peaks and valleys in B are given as follows: (a) Hg–I of HgI2 and HgI; (b) I···I of HgI2; (c) Hg···solvent; (d) I···solvent; and (e) I···solvent and Hg···solvent. The assignments for the solvent-only term (the last curve) are not shown here but were given in one of our previous publications (1).
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Fig. 5.Determination of the photodissociation pathway of HgI2 in methanol. Theoretical (red) and experimental (black) difference intensities for candidate channels are shown in qΔS(q) curves (A) and rΔS(r) curves (B). The differences (residues) between theoretical and experimental curves are also shown in blue. χ2 values for each channel from the global-fitting at 100 ps are shown. The channel HgI2 → HgI + I gives the best fit.
Footnotes
- ††To whom correspondence may be addressed at: European Synchrotron Radiation Facility 6, Rue Jules Horowitz BP 220, Grenoble Cedex 38043, France. E-mail: wulff{at}esrf.fr
- ‡‡To whom correspondence may be addressed at: Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong-dong, Yuseong-gu, Daejeon, 305-701, South Korea. E-mail: hyotcherl.ihee{at}kaist.ac.kr
- © 2006 by The National Academy of Sciences of the USA
