Measuring cluster temperatures via kinetic-energy release

We use photodissociation of neutral sodium clusters to measure the recoil p attern of the fragmentation products. The time dependence of the depletion curves reflects the kinetic-energy release that depends on the internal ene rgy, or the temperature, of the cluster. The fragmentation process is treat ed parallel to the Weisskopf statistical theory of the disintegration of co mpound nuclei. From the kinetic energies of evaporation, we are able to det ermine the temperatures of both the daughter and mother clusters. For Na-20 the temperature is found to be T=440+/-65 K, which is in good agreement wi th an estimate based on the evaporative ensemble model. The measured temper ature is slightly larger than that found for large ionic clusters. Branchin g ratios for the evaporation of sodium dimers and monomers from hot neutral clusters are estimated. [S1050-2947(99)01301-3].