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probing changes in the solvent motions during chemical dynamics in
Probing Changes in the Solvent Motions During Chemical Dynamics in Solution Matthew J. Ammend The Blank Research Group, Department of Chemistry University of Minnesota 63rd Ohio State University International Symposium on Molecular Spectroscopy June 19th, 2008 Resonant Pump Third-Order Raman probe Spectroscopy (RaPTORS) • resonant pump electronically excites the chromophore • nonresonant third-order Raman probe tracks changes in low-frequency solvent motions 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 1 Nonresonant Third-Order Raman – Our Probe librations collision-induced collective reorganization (diffusion) 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 2 Nonresonant Third-Order Raman – Our Probe τ / fs Time-Domain TOR Response FT 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 Frequency-Domain TOR Spectrum 3 Change in the TOR Spectrum Farrer, R.A.; Loughnane, B.J.; Deschenes, L.A.; Fourkas, J.T. J. Chem. Phys. 1997, 106, 6901-15 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 4 Coumarin 102 vs. Coumarin 153 t t t /ps 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 5 sample res, nr1, nr2, nr3 LO 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 6 1.24 mm translation of the DO rotates the relative LO phase by π radians 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 7 Phase Stability phase stability: 220 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 8 RaPTORS of C102 in acetonitrile 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 9 RaPTORS of C102 in acetonitrile 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 10 RaPTORS of C102 in acetonitrile 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 11 C102 vs. C153 C102 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 C153 12 Finite-Field MD Simulations Jansen, T.l.C., Snijders, J.G., and Duppen, K. J. Chem. Phys. 2001 114 10910-21 • modified version of the Gromacs molecular dynamics program • electric field is applied to equilibrated simulation box • linear susceptibility is calculated after each subsequent time step • the third-order response is then calculated with the following equation: 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 13 Simulations 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 14 Simulations simulation 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 experiment 15 Conclusion • conflicting RaPTORS results for Coumarin 102 and Coumarin 153 inspired modifications to the experiment allowing the phase of the signal to be measured • the local oscillator has been spatially separated from the beam crossing to eliminate any additional, unwanted pump-probe signals • the phase has been drastically downgeared allowing for better control and remarkable stability • the phase of C153 RaPTORS signal suggests that there is, in fact, some resonant component to the signal while the phase of the C102 signal confirms that it is (almost) entirely nonresonant • preliminary results from finite-field MD simulations look promising • future plans: charge transfer systems, proteins 63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008 16 Acknowledgements Dr. David Blank Dr. Mayrose Salvador Dr. Nathan Wells Dr. Andy Healy Adam Huss Francesc Molins I Domenech Anne Brownson Jon Hinke Funding: 17 18 19