Xinxin Cheng, Yao Zhang, Michael P. Minitti, Sanghamitra Deb, James Budarz, Peter M. Weber Chemistry...
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Transcript of Xinxin Cheng, Yao Zhang, Michael P. Minitti, Sanghamitra Deb, James Budarz, Peter M. Weber Chemistry...
Xinxin Cheng, Yao Zhang, Michael P. Minitti, Sanghamitra Deb, James Budarz, Peter M. Weber
Chemistry DepartmentBrown University
66th OSU International Symposium on Molecular Spectroscopy
06/21/2011
Ultrafast Structural Dynamics of Tertiary Amines upon Electronic
Excitation
h
Response to Electronic Excitation: Ammonia
h
Ground State
David M. Bishop, J. C. Leclerc and Y. Takahata, Journal of Molecular Spectroscopy, 1971, 39, 79-89
Halpern, A. M.; Roebber, J. L.; Weiss, K. J. Chem. Phys. 1968,49, 1348–1357
Excited State
laser pulse
Tertiary Amines
Ground State
Halpern, A. M.; Roebber, J. L.; Weiss, K. J. Chem. Phys. 1968,49, 1348–1357
h ?
Issues in tertiary amines:• Steric hindrance• Conformers• Intramolecular vibrational redistribution(IVR)
• What is the structural response of tertiary amines to electronic excitation?
• Can we measure it?• Observe the structure as a function of time.
Question to Ask and Our Goal
Rydberg Fingerprint Spectroscopy
Xiao Liang, Michael G. Levy, Sanghamitra Deb, Joseph D. Geiser, Richard M. Stratt*, Peter M. Weber,*Journal of Molecular Structure 978 (2010) 250–256
EB Ry
(n )2
n: principle quantum #δ: quantum defect
BE Structure
5 KHz Rep. RateTwo color experiment
• 4ω+2ω208 nm pump (5.96 eV)416 nm probe (2.98 eV)
Jie Bao, Dissertation, 2011, page 10
Experimental Settings
PES 4ω+2ω
• A typical two-color PES of amine
Jaimie L. Gosselin,† Michael P. Minitti,† Fedor M. Rudakov,† Theis I. Sølling,‡ and Peter M. Weber*,† J. Phys. Chem. A 2006, 110, 4251-4255
(DMIPA)
3p
3s
Proposed Structural Response
h
IVR
• Tertiary amine changes from an initial pyramidal structure to a planar structure.
• Relaxation from a local energy minimum to a global minimum: an IVR process.
Fit Results
• Linear peak center shift model• Exponential peak center shift model
Linear shift
Exponential shift
(DMIPA)
Preliminary Data
compond shift amplitude (mev) shift time constant (fs)
DEMA 74(1) 95(2)
DMIPA 24(2) 133(12)
DABCO 47(1) 111(3)
CENNA 52(2) 94(6)
Summary
• The structural response of polyatomic molecules can be complex because more degree of freedom are included.
• Though complicated, the responses are observable, for instance, using Rydberg Fingerprint Spectroscopy.
• The initial motion of tertiary amines is on the order of 100fs. The response involves intramolecular vibrational redistribution and structure changes that make the amine planar and rotate the methyl groups.