Determining excitation temperature of fragmented C-60 via momentum distributions of fragments

Hot C-60 molecules under nanosecond laser excitation decay by a variety of fragmentation channels. An experimental search has been made to determine the excitation temperature of fragmented C-60 via analyzing the momentum distributions of the prompt ionic fragments C-n(+) (n <= 58). It was found that all the C-60 precursors appearing as these ionic fragments have almost the same temperature and the temperature shows little variation with the laser fluences in our limited range. The results provide a clear evidence that a first-order phase transition in the fragmented C-60 is occurring at this temperature. The value of phase transition temperature is found to be about 6050 +/- 250 K, which is in a good agreement with the most recent estimations based on the molecular dynamics simulation. This approach offers an experimental opportunity for studying the fragmentation thermodynamics of more complex polyatomic molecules under excitation temperature determined conditions.