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 Sn_N 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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PCCP “Hot Articles” 2022

Festschrift Wolgang E. Ernst

In our publication we describe and test the newly developed reaction cell of the cluster catalysis apparatus. The cell was developed to perform catalytic studies under atmospheric pressures on monodispersively deposited subnanometer clusters, which have rarely been performed so far.

To this end, the characteristics of the reaction cell are first highlighted and discussed. Due to the innovative design, arbitrary gas phase reactions can be studied in a pressure range of 50-2000 mbar and at 50-400 °C. The platinum-catalyzed CO oxidation is taken as the first reactive system and performed on a Pt(111) single crystal in the new high-pressure cell. The results of this benchmark series of experiments are in good agreement with literature results and demonstrate the capabilities of the new setup. As a prototype cluster catalyst, Pt₁₀ is deposited on TiO₂ and compared to the single crystal. Comparing the reactivity of clusters relative to its solid state counterpart, it is found that an up to six times higher reactivity per active site can be achieved by Pt with lower activation energy. In summary, the results demonstrate the capabilities of cluster catalysis even under real atmospheric conditions.

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