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Ultrafast Diffraction of Transient Molecular Structures in Radiationless Transitions

Lobastov, Vladimir A. and Srinivasan, Ramesh and Goodson, Boyd M. and Ruan, Chong-Yu and Feenstra, Jonathan S. and Zewail, Ahmed H. (2001) Ultrafast Diffraction of Transient Molecular Structures in Radiationless Transitions. Journal of Physical Chemistry A, 105 (50). pp. 11159-11164. ISSN 1089-5639. doi:10.1021/jp013705b.

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Radiationless transitions in molecules are ubiquitous in photophysical, chemical, and biological systems. Because such transitions are usually ultrafast in nature, the determination of transient structures is extremely difficult, particularly for complex molecules with many degrees of freedom. Here, we report the direct determination of the molecular structure during the ultrafast, nonradiative transition in aromatic pyridine, excited above the so-called channel three threshold, which marks the onset of an anomalous decay. The approach we invoked is ultrafast electron diffraction (UED), developed in this laboratory to image transient molecular structures in real time. The diffraction results reveal the breakage of “old bonds” near 1.4 and 2.4 Å and the formation of “new bonds” near 1.3 and 1.5 Å and at distances greater than ∼3.5 Å, thus permitting the dominant intermediate species to be identified. Unexpectedly, a ring-opened diradical structure resulting from C−N bond scission was observed and was found to form with a rate of (17 ps)-1. This hitherto unknown intermediate must be considered as a new channel for energy dissipation in pyridine and possibly analogous molecules. These results represent a clear demonstration of the potential of UED for studying structural dynamics of radiationless transitions in complex molecular systems.

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Goodson, Boyd M.0000-0001-6079-5077
Additional Information:© 2001 American Chemical Society. Received: October 3, 2001. Publication Date (Web): November 9, 2001. We gratefully acknowledge Hyotcherl Ihee for helpful discussions. We thank E. W.-G. Diau, T. I. Sølling, and C. Kötting for help with the quantum chemical calculations. This work was supported by the National Science Foundation and the Air Force Office of Scientific Research.
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Air Force Office of Scientific Research (AFOSR)UNSPECIFIED
Issue or Number:50
Record Number:CaltechAUTHORS:20160819-085640574
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Official Citation:Ultrafast Diffraction of Transient Molecular Structures in Radiationless Transitions Vladimir A. Lobastov, Ramesh Srinivasan, Boyd M. Goodson, Chong-Yu Ruan, Jonathan S. Feenstra, and Ahmed H. Zewail The Journal of Physical Chemistry A 2001 105 (50), 11159-11164 DOI: 10.1021/jp013705b
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69771
Deposited By: Ruth Sustaita
Deposited On:23 Aug 2016 18:45
Last Modified:11 Nov 2021 04:19

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