1. Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, 79104 Freiburg, Germany
2. Department of Chemistry, Boston College, Merkert Chemistry Center, Chestnut Hill, Massachussetts 02467-3860, USA
3. Fakultät für Physik, Albert-Ludwigs-Universität , 79104 Freiburg, Germany

Correspondence to: Horst Prinzbach¹ Correspondence and requests for material should be addressed to H.P. (e-mail: Email: horst.prinzbach@orgmail.chemie.uni-freiburg.de).

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 observed^{3, 4, 5, 6} so far. Here we show that the cage-structured fullerene C₂₀ can be produced from its perhydrogenated form (dodecahedrane C₂₀H ₂₀) 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.