Abstract
Mass distributions of negative cluster ions of copper (Cu) n −, silver (Ag) n −, and gold (Au) n − obtained by the bombardment of metal sheets with Xe ions were investigated up to cluster size n = 250 and were compared with those of the positive cluster ions. The mass spectra were obtained under the same conditions as previously employed to study positive cluster ions and the behaviour of the mass distributions of the negative cluster ions were very similar to those of the positive cluster ions. The ion intensity of the clusters decreased with increasing cluster size, n, and two types of anomaly were observed. One was a regular variation of the ion intensity between odd and even values of n, where the intensity of odd- n clusters was greater than that of even- n, which is explained by pairing of the electrons. The other anomaly was a discontinuous variation of ion intensity at specific numbers n = 1, 7, 17, 19, 33, 39, 57, 91, 137, and 197. In the mass spectra of positive cluster ions, these were 3, 9, 19, 21, 35, 41, 59, 93, 139, and 199. It is confirmed from this intensity behaviour that a one-electron shell model can be applied to explain the stability of those metal clusters in which s valence electrons are bound in a spherically symmetric potential well.
Published Version
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