Clusters of fullerene molecules

Intensity anomalies have been observed in the mass spectra of (${\mathrm{C}}_{60}$ ${)}_{\mathit{n}}^{+}$ and (${\mathrm{C}}_{70}$ ${)}_{\mathit{n}}^{+}$ clusters for n=13, 19, 23, 35, 39, 43, 46, 49, and 55. These numbers indicate that the closed shell clusters n=13 and 55 are probably icosahedra. The molecules in an incomplete shell seem to undergo a structural transition as the shell fills, similar but not identical to the transition proposed for Ar cluster ions.