Research Articles

On the Shape of C6H6+

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Science  22 Mar 1996:
Vol. 271, Issue 5256, pp. 1698-1702
DOI: 10.1126/science.271.5256.1698


The benzene molecule serves as a benchmark among the aromatic hydrocarbons and has been the subject of numerous experimental and theoretical studies. Despite such intensive investigations, the precise structure of the benzene cation (C6H6+) is not known. Now, experiments measuring high-resolution state-to-state threshold photoionization spectra of benzene concretely establish the terms of vibronic levels in the distorted cation that are split by higher order Jahn-Teller coupling between its 2E1g electronic ground state and ν6 e2g in-plane ring-bending vibrational mode. This assignment, in turn, sets the absolute energy phase of the vibronic pseudorotation in this coordinate and thereby offers a definitive experimental determination of the shape of the benzene cation.