| The concept of Lewis acids and bases has been successfully used to predict trends in the interaction of ligands with metal centers in solution phase chemistry and in gas phase chemistry. In addition various authors have used Lewis acid-base concepts to explain observed surface chemistry. However a rigorous test of the ability of Lewis acid-base concepts to predict surface chemistry was lacking. The goal of this work was to characterize the interaction of seven probe molecules with five different chemically modified molybdenum (100) surfaces in order to rigorously test the applicability of Lewis acid-base concepts to surface-adsorbate interactions.;Carbon and oxygen modify the surface electronic structure creating Lewis acid adsorption sites. The more oxidized the surface metal atoms are, the stronger they bond to the Lewis bases. The trend is just the opposite for the pi acids, carbon monoxide and trifluoropropene, because backbonding with the more oxidized metal atoms is weaker. The desorption energies for all of the probe molecules on the sulfur modified surface were very low.;The five different surface modifiers studied were: 1.5 monolayers oxygen, 1.2 monolayers oxygen, 1.0 monolayers oxygen, 1.0 monolayers carbon, and.8 monolayers sulfur. The seven probe molecules studied were ethene, propene, 3,3,3-trifluoropropene, ammonia, dimethylether, phosphine and carbon monoxide. The desorption energies for each probe molecule on each modified surface were determined by thermal desorption spectroscopy, and the probe molecule was found to adsorb dissociatively in only five cases. |
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