Determining C2 binding energies from KERDs for C80+ and C82+ fullerenes and their endohedrals

Kinetic Energy Release Distributions (KERDs) have been measured for the C-2 evaporation from a series of fullerenes including C-80(+) and its endohedral compounds, Sc3N@C-80(+) and Ti-2@C-80(+). We have employed Finite Heat Bath Theory (FHBT) to analyze the measured KERDs and to deduce the C2 binding energies. Were-evaluated previously measured binding energies for C-82(+), La@C-82(+), and Tb@C-82(+) in the light of recent findings that fragmentation of fullerene ions proceeds via a very loose transition state. This procedure demonstrates a substantial increase in the binding energy on going from C-82(+), to La@C-82+ & Tb@C-82(+). The KERDs for all three ions, C-80(+), Sc3N@C-80(+), and Ti-2@C-80(+) are nearly overlapping and the C2 binding energies are equal within experimental error. The binding energy deduced for C-80(+) is surprisingly high. C-82(+) on the other hand has nearly the same stability as C-78(+). These results indicate that C-80 is a magic number. The results will be discussed in the light of proposed structures for the various compounds and the reliability of data deduced from KERDs. (C) 2003 Elsevier Science B.V. All rights reserved.