On the unimolecular fragmentation of C60+ fullerene ions: The comparison of measured and calculated breakdown patterns

Abstract

The stability of singly charged C60+ fullerene ions, produced by electron impact ionization of C60, has been studied as a function of the electron energy and the time elapsed from ionization in a Nier-type ion source/double-focusing, sector-field mass spectrometer system. A huge kinetic shift of more than 34 eV (dependent on the observation time) was observed for the dissociation process C60+→C58++C2. The ionization efficiency curves for C58+, C56+, and C54+ fragment ions have been recorded with an energy resolution of approximately 0.5 eV. This allowed us to construct a time-resolved breakdown graph of the decaying C60+ fullerene ion. Two different methods, i.e., the finite heat bath model of Klots and the Rice–Ramsperger–Kassel–Marcus (RRKM) expression, have been used to calculate the decay rates and the breakdown graph of the C60+ ion, and the results of the calculation have been compared with the experimentally obtained breakdown graph. The best fit leads to a dissociation energy (C58+−C2) of 7.1±0.4 eV. This value is somewhat larger than the dissociation energies predicted earlier from the kinetic energy release distributions, and possible reasons for this difference are discussed in this paper. Using a quasithermochemical cycle the dissociation energy (C58−C2) of the neutral C60 molecule has been estimated to be 7.64±0.4 eV.