Ion mobility studies of metal-coated fullerenes

Ion mobility measurements have been used to examine the structures and frag mentation processes of NbxC60+ complexes with up to five niobium atoms. Our results confirm the observations of Martin and collaborators that loss of C-3 is an important fragmentation process for complexes with x greater than or equal to 3. However, ion mobility measurements for NbxC60+ complexes an d their NbxC60-3n+ fragments show that they are all fullerenes. It is likel y that the NbxC60-3n+ fragments with an odd number of carbon atoms are stab ilized by a niobium atom occupying the defect site in the fullerene cage, a nd that this stabilization makes C-3 loss energetically favored over the us ual fullerene dissociation process of C-2 loss. Detailed analysis of the io n mobility measurements shows that the niobium atoms in the NbxC60+ complex es are clustered together on the fullerene surface. At high injection energ ies a structural transformation occurs for Nb2C60+ and one of the niobium a toms apparently moves to an endohedral position. This process does not occu r for NbC60+, but an analogous structural transformation appears to occur f or all complexes with x > 2. (C) 1999 Elsevier Science B.V.