Measuring cluster temperatures via kinetic-energy release

We use photodissociation of neutral sodium clusters to measure the recoil pattern of the fragmentation products. The time dependence of the depletion curves reflects the kinetic-energy release that depends on the internal energy, or the temperature, of the cluster. The fragmentation process is treated parallel to the Weisskopf statistical theory of the disintegration of compound nuclei. From the kinetic energies of evaporation, we are able to determine the temperatures of both the daughter and mother clusters. For Na₂₀ the temperature is found to be T=440±65 K, which is in good agreement with an estimate based on the evaporative ensemble model. The measured temperature is slightly larger than that found for large ionic clusters. Branching ratios for the evaporation of sodium dimers and monomers from hot neutral clusters are estimated.