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Gas-phase production and photoelectron spectroscopy of the smallest fullerene, C20

Abstract

Fullerenes are graphitic cage structures incorporating exactly twelve pentagons1. The smallest possible fullerene is thus C20, which consists solely of pentagons. But the extreme curvature and reactivity of this structure have led to doubts about its existence and stability. Although theoretical calculations have identified, besides this cage, a bowl and a monocyclic ring isomer as low-energy members of the C20 cluster family2, only ring isomers of C20 have been observed3,4,5,6 so far. Here we show that the cage-structured fullerene C20 can be produced from its perhydrogenated form (dodecahedrane C20H20) by replacing the hydrogen atoms with relatively weakly bound bromine atoms, followed by gas-phase debromination. For comparison we have also produced the bowl isomer of C20 using the same procedure. We characterize the generated C20 clusters using mass-selective anion photoelectron spectroscopy; the observed electron affinities and vibrational structures of these two C20 isomers differ significantly from each other, as well as from those of the known monocyclic isomer. We expect that these unique C20 species will serve as a benchmark test for further theoretical studies.

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Figure 1: Isomers of C20.
Figure 2: Preparation of precursors for cage 1 and bowl 2.
Figure 3: Cation mass spectrum of [C20HBr13]; 70-eV electrons were used for ionization.
Figure 4: Anion mass spectra of [C20HBr13] (a) and [C20HBr9] (b).
Figure 5: Photoelectron spectra of the mass-selected C-20 clusters.

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Acknowledgements

We thank J. Leonhardt, G. Leonhardt-Lutterbeck, S. Ruf and C. Warth for technical assistance, and G. Seifert, S. Larsson and R. C. Haddon for discussions. This work was supported by the BASF AG, the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and the US National Science Foundation.

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Correspondence to Horst Prinzbach.

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Prinzbach, H., Weiler, A., Landenberger, P. et al. Gas-phase production and photoelectron spectroscopy of the smallest fullerene, C20. Nature 407, 60–63 (2000). https://doi.org/10.1038/35024037

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