Time-resolved kinetic energy release (KER) measurements were performed on an ion trap/reflectron mass spectrometer. The average KER for C2 evaporation from C60·+ was observed to decrease with increasing precursor ion lifetime. This constitutes proof that the KER is due to the non-fixed energy in the transition state rather than to a reverse activation energy, and that the reaction takes place via a loose transition state. The data will be extended to longer lifetimes and to other cluster systems, and modelled by finite heat bath theory (FHBT). The possibility of experimentally observing phase transitions in cluster systems can now be explored.