Density functional theory investigation of gold cluster geometry and gas-phase reactivity with O_2

摘要

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 Au_9~- and Au_10~- 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 O_2 with different energies are identified on Au_10~-, and Au_11~- are predicted in agreement with frontier orbital theory. The calculated binding energies are consistent with the experimentally observed patterns in adsorption of O_2 on anionic Au clusters. The binding energy for O_2 to Au_10~- was calculated to the 19 kcal/mol, higher than for O_2 to either Au_9~- (4 kcal/mol) or Au_11~- (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 Au~_10~- cluster, approaching the calculated bond length of 1.41 angstroms for the gas--hase superoxide ion O_2~-.