Decoration of fullerenes with atoms and low-mass molecules (P 26635)

funded by FWF

Summary:

The surface of fullerenes and clusters of fullerenes represent ideal models to study the adsorption of atoms and low-mass molecules to well-defined structures. A single fullerene resembles very well carbon nanotubes or even a piece of graphene with the advantage that fullerenes can be produced with very high purity (>99.99%). This enables mass spectrometric experiments, where the number of adsorbed species can exactly by determined by simply weighing the complex. The effect of the curvature can be tuned by the size of the fullerene. Grooves between two and dimples between three fullerenes are preferential binding sites for adorbates that interact more strongly with the fullerene surface than among each other. In contrast, species with a dominant interaction among themselves, exhibit weakly perturbed cluster growth at the fullerene surface.

Carbon, gold and alkali atoms, however, form strong chemical bonds with fullerenes, leading in the former two cases to the formation of dumbbells and even chains and in the case of alkali metals to salts. High potential for hydrogen storage has been predicted for complexes of C₆₀ with lithium based on theoretical calculations. In the present project we could verify this experimentally for the system C₆₀ and cesium.

Micro-solvation of fullerene and coronene ions with helium and hydrogen clearly exhibit geometrical shell closures where the high binding energy to the first layer often results in a solid film where the solvent atoms/molecules occupy geometrically strongly confined positions. However, optical spectroscopy of helium decorated fullerene ions indicate a partial melting of the solid layer upon occupation with additional He atoms. Laser excitation of electronic transitions of C₆₀⁺ leads to the evaporation of up to several 100 adsorbed He atoms which can He atoms which can easily be observed mass spectrometrically. Our measurements confirm absorption lines of C₆₀⁺ that were recently determined via photodissociation of He-tagged fullerene ions in cryogenic ion traps. In this previous study these very same lines were also observed in astronomical spectra from diffuse interstellar clouds. For one of these lines we observed a clear difference for He attached to pentagonal or hexagonal faces. This leads to a pronounced line broadening due to statistical occupation of the two types of faces of the fullerene surface. This new kind of action-spectroscopy is way more efficient and provides deeper insight into the micro-solvation and matrix shifts of the first solvent layer than previous methods. Thus we plan to utilize this advantage in a follow-up project for the search of additional carriers of the 600 known diffuse interstellar bands.

Final Report (PDF)

List of Publications (PDF)