Mass spectrometric study of unimolecular decompositions of endohedral fullerenes

Abstract

Unimolecular decompositions of noble gas containing endohedral fullerenes as well as metallofullerenes were studied using tandem mass spectrometry techniques. Endohedral fullerenes do not lose the endohedral atom unimolecularly but fragment via the loss of C 2 units. Kinetic energy release distributions were measured for the emission of C 2 units from the positive ions of C 60, Ne@C 60, Ar@C 60, Kr@C 60, C 82, La@C 82, Tb@C 82, C 84, and Sc 2@C 84. These distributions were analyzed using both a model free approach, and a formalism developed by Klots, based on decomposition in a spherically symmetric potential. The C 2 binding energies were deduced from the models. Noble gas atoms are shown to stabilize the fullerene cage. The C 2 binding energies increase in the order: ΔE vap(C 60 +) < ΔE vap(Ne@C 60 +) < ΔE vap(Ar@C 60 +) < ΔE vap(Kr@C 60 +). Endohedral metal atoms have a strong effect on the cage binding. The C 2 binding energy in La@C 82 + is about 1.5 eV higher than that in C 82 +. The Tb atom has an even stronger effect with a binding energy of about 3 eV higher than for C 82 +. The emission of a C 2 unit from the dimetallofullerenes Sc 2@C 84 + and Tb 2@C 84 + was studied as well. Two Sc atoms have a slight destabilizing effect on C 84, whereas two Tb atoms stabilize the cage.