Anion photoelectron spectroscopy of germanium and tin clusters containing a transition- or lanthanide-metal atom; MGe _n ^- (n = 8-20) and MSn _n ^- (n = 15-17) (M = Sc-V, Y-Nb, and Lu-Ta)

The electronic properties of germanium and tin clusters containing a transition- or lanthanide-metal atom from group 3, 4, or 5, MGe _n (M = Sc, Ti, V, Y, Zr, Nb, Lu, Hf, and Ta) and MSn _n (M = Sc, Ti, Y. Zr, and Hf), were investigated by anion photoelectron spectroscopy at 213 nm. In the case of the group 3 elements Sc, Y, and Lu, the threshold energy of electron detachment of MGe _n ^- exhibits local maxima at n = 10 and 16, while in the case of the group 4 elements Ti, Zr, and Hf, it exhibits a local minimum only at n = 16, associated with the presence of a small bump in the spectrum. A similar behavior is observed for MSn _n ^- around n = 16, and these electronic characteristics of MGe _n and MSn _n are closely related to those of MSi _n. Compared to MSi _n, however, the larger cavity size of a Ge _n cage allows metal atom encapsulation at a smaller size n. A cooperative effect between the electronic and geometric structures of clusters with a large cavity of Ge ₁₆ or Sn ₁₆ is discussed together with the results of experiments that probe their geometric stability via their reactivity to H ₂O adsorption.