A deeper understanding of the physics and chemistry of clusters has been constrained by the inability to observe experimentally the structure and structural variations for size selected clusters. We report here measurements of trapped ion electron diffraction, a technique that presents the possibility to directly observe the evolution of cluster structure with size and temperature. The results of electron diffraction from C 60 ϩ ions stored in a radio-frequency Paul trap are reported. ͓S1050-2947͑99͒50305-3͔

We report an investigation of (CsI)(n)Cs (+) cluster structures (n = 30-39) studied using the recently developed technique of trapped ion electron diffraction. Contributions to diffraction from both rock salt (NaCl) and cesium chloride lattice (CsCl) derived isomeric structures are observed at size n = 32. This size can form a closed shell rhombic dodecahedron corresponding to the CsI bulk structure. All other sizes, n not equal32, are dominated by the NaCl structure. Density functional calculations and molecular dynamic simulations identify the presence of a stable CsCl lattice derived structure isomer which is consistent with these results.

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The failure of standard solid state methods to determine the structure of very small clusters has been the starting point to adapt the ion chromatography technique to cluster experiments. A new approach combining an ion drift cell and a time-of-flight mass spectrometer for cluster ion mobility measurements is described. In this publication we concentrate on the experimental set-up and the data analysis starting with the time-of-flight mass spectra. Furthermore, first results concerning relative ion mobilities for cesium iodide and sodium iodide clusters will be shown to demonstrate the feasibility of the new tandem instrument.