Mobilities of metal cluster ions: Aluminum and the electronic shell model

The mobilities of size-selected aluminum cluster ions containing 5–73 atoms have been measured using injected ion drift tube techniques. The mobilities show an apparent correlation with the electronic shell model: Clusters close to the electronic shell closings have enhanced mobilities. A structural transition appears to be associated with the shell closing with 138 valence electrons. Structural isomers were identified for a few clusters at low temperatures. But with only one exception (Al45+) the annealing temperatures of these isomers are below room temperature.