Group 14 of the periodic table is of particular interest for researchers and engineers alike due to its non-metal-to-semiconductor-to-metal transition. Tin has two stable allotropes, which represent exactly the interface between semiconductors and metals. Due to similar optical properties to silicon clusters – as to be revealed by this study – a deeper understanding of the miniaturization and cluster properties of tin is also of key interest. In this study, electrical beam deflection measurements and photodissociation spectroscopy, together with quantum chemical calculations, are applied to elucidate the geometry and electronic structure of SnN clusters with N=6-20,25,30,40.
Tin clusters show a characteristic prolate growth starting from a size of about 12 atoms, which is also reflected in the deflection profiles and absorption spectra. Here, the influence of electric dipole moments, rotational and vibrational temperature on the former and the effect of multiphoton absorption and dissociation kinetics treated in the framework of the RRKM theory on the latter were investigated. It was found that for some cluster sizes, several isomers must be present in the molecular beam simultaneously, often differing significantly in their polarity. This allows further conclusions to be drawn, e.g. on the relative energies of the cluster isomers. Experimental evidence could also be collected for dominant dissociation channels via Sn, Sn7 and Sn10 fragments. The prolate structures are then gradually replaced by quasispherical geometries in the size range of 30<N≤40, which becomes apparent from the increase in the absorption cross section and can already be understood qualitatively via classical models such as Mie-Gans theory.
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Festschrift Wolgang E. Ernst