Growth patterns in binary clusters of Group IV and V metals

Abstract

Binary clusters composed of Group IV and Group V metals (e.g., Sn/Bi) are prepared by laser vaporization of corresponding alloys in a pulsed nozzle molecular beam source. Relative abundances of these clusters are studied with laser photoionization mass spectroscopy at 193 and 157 nm. Mass spectral abundance patterns for all systems studied (Sn/Bi, Pb/Sb, Sn/As) exhibit highly nonstatistical combinations of component elements. Preferential stoichiometries follow common patterns throughout these cluster systems, which can be related to the bonding and stability of condensed phase cluster ions of these same metals. These patterns are predicted by a simple valence electron counting model.

Investigation of the stabilities of neutral and ionic lead and lead-antimony clusters under single and multiphoton ionization conditions

“…It has been proposed [13] that certain metal clusters may parallel the bonding observed for boranes, which perhaps represents the best studied approximation to the delocalized multicenter bonding expected for metal clusters, The mixed clusters observed in this study show little evidence for preferred electronic structures, as clusters with one or two antimony atoms exhibit the same magic numbers observed for pure lead clusters possessing the same total number of atoms. The low concentration of antimony in the melt makes clusters with three or more antimony atoms unlikely; thus, observation of electronically stable ions, which require a minimum of three antimony atoms, is similarly statistically unlikely.…”

“…Neutral Pb3Sb2 and Pb2Sb~ are isoelectronic with pb2-; under ionization conditions which favor neutrals, Pb3Sb + would be expected to be unusually abundant, while more severe ionization conditions which result in substantial fragmentation should favor the observed abundance of Pb/Sb + . The intensity anomalies observed by Duncan et al [13] are thus attributed to the electronic structure of the corresponding neutral or observed cluster ion, depending upon the ionization conditions employed.…”

“…Relative stabilities of neutral and ionized lead and lead-antimony clusters have been inferred from cluster ion abundances, and attempts have been made to rationalize these observations in terms of either preferred electronic or structural configurations [12][13][14]. If fragmentation is negligible, "magic numbers" observed in the mass spectrum may be properly ascribed to properties of the neutral clusters, whereas if fragmentation dominates, then particularly abundant cluster ions may represent preferred ionic structures.…”

“…Pb+4 is clearly observed at both 157 and 193 nm, though it is not detected at 248 nm. Mixed lead-antimony clusters were also obtained with the same technique [13], and analogies to borane structures and Zintl ions have been made to account for particularly abundant ions observed. As electronic structure is thus expected to play a role in determining the stabilities of these clusters, the electronic configurations of lead (6s) 2 (6p) 2 and antimony (5s)2(5p) 3 should be noted.…”

Mass spectrometry and its role in advancing cluster science

“…In Fig. 24 we show the mass distribution of Pb x Sb y and isolelectronic Sn x Bi y cluster cations of Duncan and coworkers [82] who were first to study Zintl ions in the gas phase. The magic numbers observed for Pb 2 Sb 3 + and Sn 2 Bi 3 + are consistent with (n + 1) pair valence electrons characteristic of closo-boranes.…”