Observation of multiply charged silver-cluster anions

Singly charged silver-cluster anions are produced in a laser vaporization s ource and transferred into a Penning trap. After size selection the cluster s are subjected to an electron bath in the trap, which results in the attac hment of further electrons. The relative abundance of dianions or trianions as a function of the clusters' size is analyzed by time-of-flight mass spe ctrometry. Silver-cluster dianions are observed for sizes n greater than or equal to 24 and trianions for n > 100. In addition, a detailed study of th e cluster sizes 24 less than or equal to n less than or equal to 60 shows a pronounced resistance to electron attachment for singly charged anions Ag- n(-) with a closed electronic shell, in particular Ag-29(-), Ag-33(-), and Ag-39(-). Both the threshold size for the observation of dianionic silver c lusters and the shell effects in the production yield correlate favorably w ith previous theoretical investigations of the respective electron affiniti es.