Mixed metal clusters of sodium and cesium with gold have been generated in a supersonic expansion from the mixed vapor phase. Their tendency towards binary cluster formation, relative thermodynamic stability, and ionization potentials have been experimentally and computationally investigated. The properties of the NaxAu clusters may be understood within an electronic shell model based on delocalized cluster orbitals, whereas the characteristics of CsxAu are indicative of substantial ionic interactions. Relativistic density functional calculations have been performed to elucidate the cluster electronic structure and to rationalize observed properties which may not be accounted for by the jellium model. The properties of these finite-size clusters are shown to be related to the known bulk intermetallic compounds sodium–gold and cesium–gold (cesium aurid), respectively.

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A systematic study of the mass spectra of particles formed in a supersonic nozzle expansion of Zn, Cd, and Hg vapors together with Na was performed. The particles discussed in this paper contain only one heavy atom and less than 12 Na ligands. Mass spectra from the neutral particles were generated by photoionization at five wavelengths (250, 260, 280, 300, and 320 nm) with a slit width corresponding to 16.5 and 3.3 nm, respectively. The abundances were corrected to relative differential ionization cross‐sections. Photoionization potentials for Nan M with 5 < n < 10 and M = Zn, Cd, Hg were measured. Below n = 6 no mixed clusters were found. The first abundance maximum occurred for all M at n = 8. A second maximum was with n = 16 or n = 18 (not covered in this paper). This selectivity can be rationalized by recent ab initio calculations by Fantucci et al. (J. Chem. Phys.; in press) and by jellium calculations, which give a closed shell at n = 8 with the occupations 1s21p62s2. Ionization potentials clearly show a level reversal to 1p‐2s‐1d in contrast to the homonuclear jellium with 1p‐1d‐2s. This is similar to previous results with KnMg (Kappes, M. et al., Chem. Phys. Lett., 1985, 119: 11). Molecular dynamics simulations with empirical potentials show that the heavy metal migrates to the center of a cube in the frozen asymptote of NagM. At finite temperatures and for larger central atoms, a square antiprismal arrangement seems to be more stable.

A new thermal, supersonic cluster source for the investigation of binary metal cluster formation at thermodynamically well-defined expansion conditions is described. The source consists of two separately heatable cartridges. A first cartridge can be heated up to 1220 K and the second high temperature cartridge reaches maximal temperatures of 1800 K. A temperature difference of 1000 K between the two cartridges can be maintained for at least 3 h. Clustering occurs upon supersonic expansion from a conical nozzle. This cluster source has two main applications: (a) the generation of mixed metal clusters and (b) the investigation of pure metal clusters at various expansion conditions. The performance and applications of this source are illustrated by presenting results of the heterocluster formation of mixed sodium/gold and sodium/silver heteroexpansions. In addition, the influence of the oven parameters on the internal temperatures of the generated clusters is illustrated with the example of Na2.

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