Structures of Silicon-Doped Carbon Clusters

Gas phase ion mobility measurements have been used to examine the geometries of silicon-doped carbon cluster cations, C n Si+ (n = 3−69). The observed isomers resemble those found for pure carbon clusters: linear chains, monocyclic, bicyclic, and polycyclic rings, graphite sheets, and fullerenes. Generally, the silicon atom substitutes for a carbon atom and has only a minor effect on the structure. The linear chain and monocyclic ring isomers coexist for C n Si+ clusters over a wider range than for pure carbon cluster cations. The results provide the first conclusive experimental evidence that C2 n - 1Si+ fullerenes with an even number of atoms are closed-cage structures with the silicon atom networked into the cage. For C2 n Si+ fullerenes with an odd number of atoms the silicon atom appears to be exohedral.