Thermal and non-thermal fragmentation of xenon cluster ions

The internal temperature and decay rate of free evaporating neutral and ionized xenon clusters have been calculated as a function of their size at the same moment. These functions are substantially different for the neutral and ionized clusters. In a wide range of the initial internal temperature, acquired by the neutrals in the process of the cluster formation, the results do not depend on this temperature. However, the temperature range and criterion were found, on which the results do depend. The time evolution of the decay of electron-impact ionized xenon clusters (up to 5000 atoms) has been experimentally studied in pulsed jets by the retarding potential method. Calculated properties of the evaporating fragmentation have permitted to show that non-thermal fragmentation of xenon cluster ions exists in parallel with the thermal one. With a decrease in the cluster size, the probability of the non-thermal fragmentation of xenon cluster ions increases as compared with the probability of the thermal evaporation, in agreement with the model proposed earlier. The threshold time of the non-thermal fragmentation of xenon cluster ions was found to be substantially larger as compared with that of argon cluster ions. The non-thermal fragmentation of xenon cluster ions is not due to the successive single ionization of two atoms. Ionization into the excited ion states stimulates fragmentation of the clusters.