Density functional theory investigation of gold cluster geometry and gas-phase reactivity with O2

We have conducted a density functional theory investigation into the gas-phase reactivity of small gold cluster ions in the interest of understanding gold cluster reactivity in several catalytic systems. Previously unreported geometries for Au9− and Au10− anions are obtained and reported from geometry optimizations. Predicted values of the vertical detachment energy match well with experiment, as does a rough simulation of its ultraviolet photoelectron spectrum—we found that comparison of predicted spectra with experimental data is a more sensitive analysis of geometry differences. Several binding sites for O2 with different energies are identified on Au10−, but we show that the strongest binding site and orientation is predicted by frontier orbital theory. In addition, weakly stable adsorbed states for O2 on the anion clusters Au9−, Au10−, and Au11− are predicted in agreement with frontier orbital theory. The calculated binding energies are consistent with the experimentally observed patterns in adsorption of O2 on anionic Au clusters. The binding energy for O2 to Au10− was calculated to be 19 kcal/mol, higher than for O2 to either Au9− (4 kcal/mol) or Au11− (5 kcal/mol), and the calculated O–O bond length was found to increase from its gas-phase value of 1.27 angstroms to 1.38 angstroms when adsorbed on the Au10− cluster, approaching the calculated bond length of 1.41 angstroms for the gas-phase superoxide ion O2−.