Electronic structures and properties of microclusters: cadmium and mercury

Abstract

Recently obtained experimental results on the size dependence of ionization potentials (IP), photoelectron spectra, photoionization cross-sections, and optical absorption cross-sections for mercury Hg x and cadmium Cd x clusters are presented. While small mercury clusters are weakly bound, larger mercury clusters gradually assume with increasing size (between about 13 and 70 atoms) metallic-like properties, as indicated by the trend of IPs, photoelectron spectra, as well as by the apperance of a surface-plasmon resonance excitation at 5.93 eV. A similar, but much more pronounced electronic transition is exhibited by molecular beam isolated clusters of cadmium. For instance, IP(Cd 1)IP(Cd 10)= 3.1 eV, compared with the much smaller value IP(Hg 1) IP( Hg 10) = 2.2 eV. Photoelectron spectra of mass specified neural Cd 10-clusters revealed the existence of discrete electronic shells and subshells. The electronic shell structure in neutral cadmium clusters clearly dominates mass spectrometric Cd x +-intensity distributions. Pronounced shell closings are observed for Cd 10 (with 20 valence electrons), for Cd 20, Cd 35, Cd 46, and Cd 69.