probing changes in the solvent motions during chemical dynamics in

Transcription

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
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Nonresonant Third-Order Raman – Our Probe
librations
collision-induced
collective
reorganization
(diffusion)
63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008
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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
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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
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sample
res, nr1, nr2, nr3
LO
63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008
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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
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Phase Stability
phase stability:

220
63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008

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RaPTORS of C102 in acetonitrile
63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008
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RaPTORS of C102 in acetonitrile
63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008
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RaPTORS of C102 in acetonitrile
63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008
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C102 vs. C153
C102
63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008
C153
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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
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Simulations
63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008
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Simulations
simulation
63rd OSU International Symposium on Molecular Spectroscopy June 19 th, 2008
experiment
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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
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Acknowledgements
Dr. David Blank
Dr. Mayrose Salvador
Dr. Nathan Wells
Dr. Andy Healy
Adam Huss
Francesc Molins I Domenech
Anne Brownson
Jon Hinke
Funding:
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