Kinetic energy release of C-70(+) and its endohedral cation N@C-70(+): Activation energy for N extrusion

摘要

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.