Ultrafast Structural Dynamics of Tertiary Amines upon Electronic

Ultrafast Structural Dynamics of Tertiary Amines upon Electronic Excitation Xinxin Cheng, Yao Zhang, Michael P. Minitti, Sanghamitra Deb, James Budarz, Peter M. Weber Chemistry Department Brown University 66 th OSU International Symposium on Molecular Spectroscopy 06/21/2011

Response to Electronic Excitation: Ammonia Excited State Ground State laser pulse 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

Tertiary Amines ? Ground State Issues in tertiary amines: • Steric hindrance • Conformers • Intramolecular vibrational redistribution(IVR) Halpern, A. M. ; Roebber, J. L. ; Weiss, K. J. Chem. Phys. 1968, 49, 1348– 1357

Question to Ask and Our Goal • What is the structural response of tertiary amines to electronic excitation? • Can we measure it? • Observe the structure as a function of time.

Rydberg Fingerprint Spectroscopy n: principle quantum # δ: quantum defect Xiao Liang, Michael G. Levy, Sanghamitra Deb, Joseph D. Geiser, Richard M. Stratt*, Peter M. Weber, *Journal of Molecular Structure 978 (2010) 250– 256

Experimental Settings 5 KHz Rep. Rate Two color experiment • 4ω+2ω 208 nm pump (5. 96 e. V) 416 nm probe (2. 98 e. V) Jie Bao, Dissertation, 2011, page 10

PES 4ω+2ω • A typical two-color PES of amine (DMIPA) 3 s 3 p Jaimie L. Gosselin, † Michael P. Minitti, † Fedor M. Rudakov, † Theis I. Sølling, ‡ and Peter M. Weber*, † J. Phys. Chem. A 2006, 110, 4251 -4255

Proposed Structural Response • 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.

The Process to Become Planar Structure

Fit Results • Linear peak center shift model • Exponential peak center shift model (DMIPA) Linear shift Exponential shift

Preliminary Data 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) compond

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 100 fs. The response involves intramolecular vibrational redistribution and structure changes that make the amine planar and rotate the methyl groups.

Acknowledgement Prof. Peter Weber Yao Zhang Dr. Sanghamitra Deb Dr. Michael Minitti Dr. Jie Bao Dr. Joseph Geiser Chrishtine Buehler Xiao Liang James Budarz Yan Gao Sonia Vignale Thank You!