Gas-phase production and photoelectron spectroscopy of the smallest fullerene, C-20

Fullerenes are graphitic cage structures incorporating exactly twelve penta gons(1). The smallest possible fullerene is thus C-20, which consists solel y 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 ri ng isomer as low-energy members of the C-20 cluster family(2), only ring is omers of C-20 have been observed(3-6) so far. Here we show that the cage-st ructured fullerene C-20 can be produced from its perhydrogenated form (dode cahedrane C20H20) by replacing the hydrogen atoms bwith relatively weakly b ound bromine atoms, followed by gasphase debromination. For comparison we h ave also produced the bowl isomer of C-20 using the same procedure. We char acterize the generated C-20 clusters using mass-selective anion photoelectr on spectroscopy; the observed electron affinities and vibrational structure s of these two C-20 isomers differ significantly from each other, as well a s from those of the known monocyclic isomer. We expect that these unique C- 20 species will serve as a benchmark test for further theoretical studies.