Unimolecular decay has proven to be a useful tool for studying thermal properties of small molecules and clusters. I will present a couple of experiments using the systematics associated with unimolecular decay. The first is an experiment measuring spontaneous evaporation from protonated and negatively charged water clusters that yielded size-dependent heat capacities in the size-range of five to 300 molecules per cluster. The smallest water clusters show heat capacities similar to bulk ice whereas the larger sized clusters have heat capacities between ice and liquid water. The second part will deal with particles trapped in a storage ring. Storage rings can keep charged particles in vacuum for longer times which provides the opportunity to study clusters and molecules at different times since creation. By reheating the particles with a photon at various storage times the spontaneous cooling as a function of time can be probed. Two similar experiments with different results will be presented from such measurements; the radiative and thermionic emission cooling rates for the relatively large molecule C60- and the cooling power and energy distribution from the much smaller C5- cluster.
Université Toulouse III - Paul Sabatier - Bat. 3R4 - 118 route de Narbonne - 31062 Toulouse Cedex 09 - France