| The work detailed in this thesis focuses on the production, characterization, and reactivity of early transition metal (Mo and Ti) sulfide and carbide clusters. In their bulk form, these materials are known to be active catalysts for a wide range of heterogeneous reactions. On the nanoscale, these materials form unique structures and have modified chemical properties. To examine nanostructured forms of these materials, a new size-selected cluster beam apparatus was constructed to study the reactivity of clusters in the both the gas-phase and deposited on solid surfaces. The apparatus contains a magnetron cluster source capable of generating gas-phase cation clusters of pure metals and metallic compounds, a high-mass quadrupole mass-filter for mass-selection, a hexapole collision cell to study gas-phase reactivity, and an ultrahigh vacuum chamber for deposition studies.;In initial studies on a separate instrument, neutral molybdenum carbide and sulfide clusters were produced using laser ablation and detected using time-of-flight mass spectroscopy. A wide range of stoichiometries were observed including the magic number clusters Mo8C12 + and Mo6S4+. The effect of laser fluence on the cluster distributions was also studied and interpreted using a qualitative kinetic model.;Using the newly designed instrument, the gas-phase reactivity of several mass-selected clusters was studied. The Ti8C12 + Met-Car was reacted with CS2, OCS, and SO2 with the observed products ranging from association to break down of the met-car cluster. The interaction of CO and NH3 with the M4S 6+ (M = MO, W) clusters were also studied and found to adsorb intact on the exposed metal sites. Density Functional Theory was used to better understand the observed products in both cases.;MoxSy clusters (x/y = 4/6, 6/8) were mass-selected and deposited on a Au(111) single crystal. The presence of deposited clusters was confirmed using Auger Spectroscopy while x-ray photoelectron spectroscopy was used to probe the electronic structure of the cluster-covered surface. Temperature Programmed Desorption (TPD) of carbon-13 labeled CO shows cluster-dependent desorption peaks which were used to estimate the CO binding energies. The TPD spectra are also found to depend on annealing temperature, which suggest surface modifications or cluster decomposition at higher temperatures. |
