Photodissociation kinetics of aluminum cluster ions: Determination of cluster dissociation energies

Abstract

The photodissociation of aluminum clusters, Al+n (n=7–17), has been studied over a broad energy range (1.88–6.99 eV). Measurements of the lifetimes of the photoexcited clusters are described. Dissociation energies have been determined by comparing the measured lifetimes with the predictions of a simple RRKM model. The dissociation energies show an overall increase with cluster size, but there are substantial oscillations around n=7–8 and n=13–15. Cluster cohesive energies are derived from these results and from previous measurements of the dissociation energies of the smaller clusters. The cohesive energies of the larger clusters (n>6) are in good agreement with the predictions of a simple model based on the bulk cohesive energy and the cluster surface energy. However, the cohesive energies are substantially larger than the results of recent ab initio calculations. The photodissociation spectrum of Al+8 has been measured and shows a broad absorption feature with a maximum ∼470 nm.