Multisequential photofragmentation of size-selected gold cluster ions

Time-resolved fragmentation measurements have been performed on stored, size-selected gold cluster ions Aun+ (n=17-21) that have been excited up to 15 eV by multiphoton absorption. These excitation energies are far above the clusters' dissociation thresholds and initiate multistep sequential unimolecular dissociation by evaporation of neutral monomers. The measurements allow for the determination of a combination of kinetic-energy release and radiative cooling of the excited clusters. Also, previously determined model-independent values of the cluster dissociation energies are confirmed by the present measurements. The data are consistent with thermal values of the kinetic-energy release with no significant radiative cooling of the excited clusters