CLUSTERS OF DIVALENT ELEMENTS - ELECTRONIC-PROPERTIES OF CDX-AGGREGATES

We have recently succeeded in generating and detecting neutral cadmium clusters Cd(x) (x < 80) in a seeded supersonic molecular beam. The mass spectrometric abundances of photoionized clusters exhibit remarkable intensity variations. There are large intensity ratios for Cd10/Cd11 as well as Cd20/Cd21 indicating the closing of electronic shells with 20 and 40 electrons. The photoelectron spectra of neutral cadmium clusters show the formation and filling of shells, indeed. Discrete electronic states (2S2) have been observed directly in the photoelectron spectra of mass specified Cd10 clusters. Pronounced electronic shell closings are also clearly observed for clusters with 70 electrons (Cd35), 92 electrons (Cd46), and 138 electrons (Cd69). Furthermore, we have obtained quantitative information on the size dependence of ionization potentials and photoionization cross sections. The ionization potentials (7.7 +/- 0.1 eV for the dimer Cd2 and 5.0 +/- 0.1 eV for Cd46) decrease rapidly but rather smoothly with increasing cluster size.