Theoretical determination of the absolute electron impact ionization cross-section function for silver clusters Agn (n=2-7)

A recently developed semiclassical approach (DM formalism) was used to calculate the absolute total electron-impact single ionization cross sections for silver clusters Ag-n (n=2-7) from threshold to 1000 eV. Similar to other cluster properties, a clear odd-even effect has been observed for the calculated cross sections and is ascribed to the effective electron numbers in the valence shell. The only available experimental data for comparison are partial cross sections for the production of the singly charged parent ions for the monomer up to the tetramer. No experimental data are available as yet for any larger clusters nor for the total ionization cross sections. Nevertheless, a comparison of the results of the present calculations with calculations using additivity rules applied to molecules and clusters gives valuable insight into the ionization behavior of clusters as a function of cluster size and thus elucidates the transition from a molecular-type situation where the cross sections of the constituents are additive to a cluster-type situation where geometric effects lead to a n(2/3)-dependence in the limit of large cluster sizes n. (C) 1999 American Institute of Physics. [S0021-9606(99)00127-0].