Latest findings on the photoionization of Met-Cars

An overview of our latest findings on the photoionization of metallocarbohe drene clusters (Met-Cars) is presented. The ionization potentials (IPs) of titanium and zirconium Met-Cars of the stoichiometry Ti8-xZrxC12 (x = 0-4, 8) were determined by studying their photoionization efficiency spectra nea r threshold. It was found that the IPs are about 4 eV and decrease smoothly as the Ti/Zr ratio decreases. Comparison of the determined IPs with those predicted by theoretical calculations by other groups suggests that the geo metry of the Met-Cars is that of the tetrahedral cage structure with T-d sy mmetry, assuming a high degree of accuracy in the IP calculations. In anoth er experiment, we investigated the mechanism of the delayed ionization of b oth single- and binary-metal Met-Cars. Using a reflectron time-of-night mas s spectrometer with a modified Wiley-McLaren double acceleration region, we measured ionization rates arising from the electron emission of Met-Cars c omposed of various transition metals under different photoionization condit ions, which led to the conclusion that a thermionic emission mechanism domi nantly contributes to the delayed ionization.