Kinetic Energy Release of C70+ and Its Endohedral Cation N@C70+: Activation Energy for N Extrusion

Unimolecular decomposition of C 70 + and its endohedral cation N@ C 70 + were studied by high-resolution mass-analyzed ion kinetic energy (MIKE) spectrometry. Information on the energetics and dynamics of these reactions was extracted. C 70 + dissociates unimolecularly by loss of a C 2 unit, whereas N@C 70 + expels the endohedral N atom. Kinetic energy release distributions (KERDs) in these reactions were measured. By use of finite heat bath theory (FHBT), the binding energy for C 2 emission from C 70 + and the activation energy for N elimination from N@C 70 + were deduced from KERDs in the light of a recent finding that fragmentation of fullerene cations proceeds via a very loose transition state. The activation energy measured for N extrusion from N@C 70 + was found to be lower than that for C 2 evaporation, higher than the value from its neutral molecule N@C 70 obtained on the basis of thermal stability measurements, and coincident with the theoretical value. The results provide confirmation that the proposed extrusion mechanism in which the N atom escapes from the cage via formation of an aza-bridged intermediate is correct.