We report a combined experimental and theoretical study investigating small zinc oxide clusters. A laser vaporization source and a time-of-flight (TOF) mass spectrometer are employed to produce and identify anionic clusters in the Zn(n)O(m) (n = 1-6, m = 1-7) size regime. The adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of Zn(3)O(3)(-) and Zn(3)O(4)(-) clusters are determined via anion photoelectron spectroscopy. We have utilized density functional theory (DFT) calculations to explore the possible geometries of neutral and anionic Zn(3)O(m) (m = 3-5) clusters, while the theoretical ADE and VDE values are compared with experimental results. The experimentally observed relative abundances among the Zn(3)O(m)(-) (m = 3-5) clusters are investigated through calculations of the detachment energies, dissociation energies, and HOMO-LUMO gaps. We find that the Zn(3)O(3) cluster maintains enhanced stability compared to their oxygen-rich counterparts. Furthermore, by coupling the experimentally obtained photoelectron angular distributions of Zn(3)O(3)(-) and Zn(3)O(4)(-) with electronic structure calculations, the nature of the highest occupied molecular orbitals is discussed, with the goal of aiding the isolation (ligand-capped)/deposition of these building blocks.

Evolution of electronic properties and the nature of bonding of the 4d-transition metal silicides (ZrSi, NbSi, MoSi and PdSi) are discussed, revealing interesting trends in the transition metal-silicon interactions across the period. The electronic properties of select transition metal silicide diatomics have been determined by anion photoelectron imaging spectroscopy and theoretical methods. The electron binding energy spectra and photoelectron angular distributions obtained by 2.33 eV (532 nm) photons have revealed the distinct features of these diatomics. The theoretical calculations were performed at the density functional theory (DFT) level using the unrestricted B3LYP hybrid functional and at the ab initio unrestricted coupled cluster singles and doubles (triplets) (UCCSD(T)) methods to assign the ground electronic states of the neutral and anionic diatomics. The excited electronic states were calculated by the DFT (TD-DFT)/UB3LYP method. We have observed that the valence molecular orbital configuration of the ZrSi and NbSi anions are significantly different from that of the MoSi and PdSi anions. By combining our experimental and theoretical results, we report that the composition of the highest occupied molecular orbitals shift from a majority of transition metal s- and d-orbital contribution in ZrSi and NbSi, to mainly silicon p-orbital contribution for MoSi and PdSi. We expect these observed atomic scale transition metal-silicon interactions to be of increasing importance with the miniaturization of devices approaching the sub-nanometer size regime.

Cooperative reactivity plays an important role in the oxidation of CO to CO(2) by palladium oxide cations and offers insight into factors which influence catalysis. Comprehensive studies including guided-ion-beam mass spectrometry and theoretical investigations reveal the reaction products and profiles of PdO(2)(+) and PdO(3)(+) with CO through oxygen radical centers and dioxygen complexes bound to the Pd atom. O radical centers are more reactive than the dioxygen complexes, and experimental evidence of both direct and cooperative CO oxidation with the adsorption of two CO molecules are observed. The binding of multiple electron withdrawing CO molecules is found to increase the barrier heights for reactivity due to decreased binding of the secondary CO molecule, however, reactivity is enhanced by the increase in kinetic energy available to hurdle the barrier. We examine the effect of oxygen sites, cooperative ligands, and spin including two-state reactivity.

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