Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S01: Focus Session: Understanding Photochemistry through Molecular Imaging
10:30 AM–12:30 PM,
Thursday, June 3, 2021
Chair: Spiridula Matsika, Temple University
Abstract: S01.00005 : Substituent and conformer effects on photochemistry investigated by ultrafast electron diffraction and excited state wavepacket simulations*
11:36 AM–11:48 AM
Live
Presenter:
Thomas J Wolf
(SLAC - National Accelerator Laboratory)
Author:
Thomas J Wolf
(SLAC - National Accelerator Laboratory)
Collaborations:
Phellandrene UED collaboration: E. G. Champenois, D. M. Sanchez, A. Attar, M. Centurion, J. P. Cryan, R. Forbes, M. Gühr, K. Hegazy, M. Hoffmann, F. Ji, S. Saha, R. K. Li, Y. Liu, M.-F. Lin, D. Luo, D. Mayer, B. Moore, M. Nie
We have investigated photochemical ring-opening dynamics in the molecule 1,3-cyclohexadiene (CHD) and its substituted derivatives α-phellandrene (αPh) and α-terpinene with specific sensitivity to the nuclear structure evolution using MeV ultrafast electron diffraction and ab initio multiple spawning (AIMS) simulations. In CHD, we find rapid ring-opening within < 200 fs upon internal conversion through a conical intersection with the electronic ground state.
Substitution of the ring at the position of ring-opening with an isopropyl group as in α-phellandrene has far-reaching consequences for the photochemical dynamics. The substitution leads to the presence of several conformers of which we observe three in our static diffraction measurements. These three only differ by the rotation of the isopropyl group around the bond to the carbon ring. Our time-resolved experiments show a considerably slower appearance of the ring-opening signature in αPh than in CHD. Comparison with AIMS simulations only yields a high level of agreement if all three conformers are considered. The simulations reveal substantial differences in nature and time scale of the photochemical dynamics between the conformers. This marks to our knowledge the first real-time observation of conformer-specific photochemical dynamics.
*This work was supported by the U.S. Department of Energy, Office of Sciences, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.
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