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 C2 units. Kinetic energy release distributions were measured for the emission of C2 units from the positive ions of C60, Ne@C60, Ar@C60, Kr@C60, C82, La@C82, Tb@C82, C84, and Sc2@C84. 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 C2 binding energies were deduced from the models. Noble gas atoms are shown to stabilize the fullerene cage. The C2 binding energies increase in the order: ΔEvap(C60+) < ΔEvap(Ne@C60+) < ΔEvap(Ar@C60+) < ΔEvap(Kr@C60+). Endohedral metal atoms have a strong effect on the cage binding. The C2 binding energy in La@C82+ is about 1.5 eV higher than that in C82+. The Tb atom has an even stronger effect with a binding energy of about 3 eV higher than for C82+. The emission of a C2 unit from the dimetallofullerenes Sc2@C84+ and Tb2@C84+ was studied as well. Two Sc atoms have a slight destabilizing effect on C84, whereas two Tb atoms stabilize the cage.