Multilayer metal coverage of fullerene molecules

Intensity anomalies in the mass spectra of clusters with composition ${\mathrm{C}}_{60}$${\mathit{M}}_{\mathit{x}}$ and ${\mathrm{C}}_{70}$${\mathit{M}}_{\mathit{x}}$ (x=0–500; M∈{Ca,Sr,Ba}) seem to be caused by the completion of metal layers around a central fullerene molecule. The first layer is complete when one metal atom is situated above each of the 32 or 37 rings of the fullerene cage. This property appears to make it possible to ‘‘count the rings’’ of fullerenes. The first and additional layers are described in terms of a periodically reoccurring structure having icosahedral symmetry.