Electron impact ionization of gas phase silver clusters Ag,, n<36 has been achieved in the threshold region. The vertical ionization potentials in this region clearly demonstrate the evidence of shell effects as well as a distinct even-odd oscillation up to n-~ 20. Their general size dependence is somewhat different from that of the alkali metal clusters due to the presence of the delectrons.

Small noble metal clusters were produced by a gas aggregation technique and were investigated mass spectrometrically using electron ionizing energies ranging from 100 eV down to the threshold region. For energies above approximately 20 eV electronic effects are displayed, that characterize a stable cationic distribution, i.e. enhanced stability is found for odd numbered clusters posessing an even number of electrons, furthermore, shell closing appears at n = 3, 9, 21… On the other hand, the electronic effects found while investigating the threshold energy region have to be attributed to neutral clusters, i.e. even numbered clusters are more stable.–The vertical ionization potentials in this region clearly demonstrate the manifestations of shell effects as well as distinct even‐odd oscillations. For both Ag and Au a dramatical drop in the ionization potential is observed from dimer to trimer. The overall size‐dependence of the ionization energies differs from that of alkali clusters due to the presence of d‐electrons.

Abstract. The mass spectra of silver-and gold-clusters, generated by a gas aggregation technique and ionized by electron impact, reveal anomalies in the relative abundance of both singly and multiply charged clusters. Concentration maxima for singly charged species Ag, + and Au, + (n = 3, 9, t9, (21), 35) are in agreement with experimental data of Katakuse and the predictions from the electronic shell model. The observed anomalies in the abundance spectra of doubly charged silver and gold clusters as well as triply charged silver cluster ions are explained in terms of electronic shell closing.

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