Photoelectron spectroscopy of tin and lead cluster anions: Application of halogen-doping method

Electronic properties of tin (Sn) and lead (Pb) cluster anions were studied using photoelectron spectroscopy (PES) with a magnetic bottle-type electron spectrometer, where the feasibility of a halogen-doping method we recently developed was explored. The binary cluster anions containing a chlorine atom (Cl) were produced by a laser vaporization of a target rod in a He carrier gas mixed with a small amount of CCl₄ gas. Comparing the PES of Sn_nCl^- and those of Sn^-_n, it was found that the doped Cl atom in Sn_nCl^- deprives each Sn^-_n cluster of the excess electron without any serious rearrangement of the Sn_n framework, which is similar to our previous work on Si_nF^- and Ge_nF^-. The halogen-doping method enables us to reveal the HOMO-LUMO gap of the corresponding neutral cluster of the Sn_n clusters, showing that the Sn_n clusters are semiconductor clusters, especially below n=30, similar to the Si_n and the Ge_n clusters. For the Pb_n clusters, however, the halogen-doping method was inapplicable, which implies that the Pb_n clusters are different from the other group-14 clusters, probably exhibiting a metallic nature.