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Experimental probing of conical intersection dynamics in the photodissociation of thioanisole

Nature Chemistry volume 2, pages 627–632 (2010)Cite this article

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Abstract

Chemical reactions that occur in the ground electronic state are described well by invoking the Born–Oppenheimer approximation, which allows their development to be rationalized by nuclear rearrangements that smoothly traverse an adiabatic potential energy surface. The situation is different, however, for reactions in electronically excited states, where non-adiabatic transitions occur between adiabatic surfaces. The conical intersection, in which two adiabatic surfaces touch, is accepted widely as the dynamic funnel for efficient non-adiabatic transitions, but its direct experimental probing is rare. Here, we investigate the photodissociation of thioanisole and observe a striking dependence of the relative yields of two reaction channels on the photoexcitation energy as indicated by a dynamic resonance in the product branching ratio. This results from the interference of two different adiabatic states that are in close proximity in the region of a conical intersection. The location of the observed resonance on the multidimensional potential energy surface thus reveals the nuclear configuration of the conical intersection and its dynamic role in the non-adiabatic transition.

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Figure 1: The three lowest diabatic potential energy curves of thioanisole along the S–CH3 bond elongation coordinate.
Figure 2: The S1 vibronic levels, the total •CH3 (v = 0) fragment yield and the / branching ratio plotted as a function of the photoexcitation energy.
Figure 3: Dynamic observables of products from the excited thioanisole near the conical intersection region.

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Acknowledgements

We thank Y.S. Lee and H. Choi for discussions, and assistance from J. Yoon and S. Han is appreciated. This work was supported by the National Research Foundation of Korea (2010-0001635, –0000068, –0015031; 313-2008-2-C00401) and KAIST (high-risk high-return).

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  1. Department of Chemistry and KI for Nano-Century, KAIST, Daejeon, 305-701, Korea

    Jeong Sik Lim & Sang Kyu Kim

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  1. Jeong Sik Lim
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Contributions

J.S.L. and S.K.K. conceived and designed the experiments, J.S. Lim performed the experiments, J.S. Lim and S.K. Kim analysed and interpreted data, and J.S. Lim and S.K. Kim co-wrote the paper.

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Correspondence to Sang Kyu Kim.

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Lim, J., Kim, S. Experimental probing of conical intersection dynamics in the photodissociation of thioanisole. Nature Chem 2, 627–632 (2010). https://doi.org/10.1038/nchem.702

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