Photoelectron spectroscopy studies on the electronic structure and chemical bonding of novel atomic clusters

Clusters, consisting of a few to a few hundred atoms, constitute a class of novel microscopic systems. The physical and chemical properties of cluster in sub-nano and nano meter (up to ∼100 nm) regime strongly depend on the cluster size and shape, which forms the foundation for nanoscience. Gas-phase techniques are advantageous in probing this size range, permitting systematic examination of quantum size effects atom-by-atom without the influence of a substrate. Photoelectron spectroscopy of size-selected anions is a particularly powerful technique to provide cluster electronic structure information and follow the evolution from discrete molecular features to bulk band structures. Advances in our laboratory to improve the energy resolution of the photoelectron spectroscopic technique and to control the cluster temperatures have allowed us to obtain well-resolved electronic features for a wide range of atomic clusters. This thesis focuses on studies of the electronic structures and chemical bonding of Al and Au based cluster systems. Small Au and Au-alloy clusters have proved to possess unusual structures and chemical bonding. Due to the strong relativistic effect, small gold cluster anions surprisingly possess two-dimensional planar structures up to twelve atoms. Combining high-level theoretical calculation with photoelectron spectra, we have discovered a series of highly stable and symmetric clusters with large energy gaps and high chemical stability, such as PbAl12, Au20, Mo Au12, W Au12, and SiAu4. Studies on Si-Au alloy clusters led to the discovery of Au-H analogy. We found that the structure and chemical bonding of SimAun-clusters ( m = 1-2 and n = 2-4) are very similar to the corresponding SimHn- molecules, thus proving the capability of Au to form covalent bonds similar to H.