The interaction of C-60(+) and C-70(+) ion beams with a surface of highly oriented pyrolitic graphite was investigated by probing the ionization and fragmentation rates of scattered species within a time window of 20 mu s following impact. Neutralization/reionization and fragmentation behavior was observed and followed by a pulsed deflection field applied to the surface at variable delays after the collision event. An almost complete collisional neutralization of the incident projectile was found. For an impact energy of 140-180 eV, a significant part of the scattered species was found to reionize by delayed electron emission within the experimental time window. The associated reionization and fragmentation kinetics were modeled with a system of differential equations assuming a simple unimolecular reaction diagram. Rate constants for delayed ionization and fragmentation were calculated as functions of internal energy and respective activation energies with the "finite heat bath" model (Klots) and the Rice-Ramsperger-Kassel-Marcus expression, respectively. The calculated and measured (deflection field delay dependent) ion intensities were compared in a fit procedure. The best fit led to an activation energy for the fragmentation of C-60(+) (C-60(+)-->C58+C2) of 6.6 +/- 0.5 eV. This translates to an activation energy of 7.1 +/- 0.5 eV for the fragmentation of neutral C-60 (using the experimentally determined ionization potential of C-58) For C-70(+) we obtained an identical (within error) activation energy for fragmentation (C-70(+)-->C-68(+)+C-2) of 6.6 +/- 0.5 eV.