Untersuchung der Wachstumssequenzen kleiner Cluster

Abstract

Within the scope of this thesis the structures of small clusters of salts as well as of C60 havebeen determined.Although the solid phase of cesium salts is the CsCl-structure, only CsCl- and CsI-clusterswith NaCl-structures have been found within former experiments. Consequently, there mustbe a transition from NaCl- to CsCl-type at a certain cluster size or within a certain size range.In order to find this transition, structures of NaI-, CsCl- and CsI-clusters have been determinedby measuring their ion mobility: cluster ions are pulled through a drift cell filled with helium(p=2mbar) by a weak electric field (typ. E=10V/cm). The scattering cross section can becalculated from the drift velocity and thus the geometric structure of the clusters can beobtained.From the experiments on positive and negative CsCl cluster ions as well as positive CsIcluster ions growth sequences similar to those of sodium salt clusters were obtained,indicating growth as NaCl-type structures. However, there was one exception, namely theclusters with size n=33. Their mobility can only be explained by assuming that these clustershave CsCl solid like structure.The structures of some clusters made of C60-molecules are still not well known, as there aredifferences between theoretical predictions and experimental findings. Therefore mobilities of(C60)n clusters were measured within the size range from n=1 to 20.Interpreting these data, one must consider that helium atoms scattering from concave siteson these clusters can undergo multiple collisions. The experimental findings for small (C60)nclusters agree well with the extended theoretical model. However, differences occurred forlarger clusters, probably because the intermolecular distance of the C60 molecules is not wellknown. Nevertheless, the suggested structure of (C60)13, an icosahedron, could be confirmed.