Interactions of water and oxygen molecules with gold clusters

The interaction of water and oxygen molecules with neutral gold clusters, Au$_{n}$ for n=2-8, is investigated using the first- principles calculations based on the density functional theory with generalized gradient correction. The O$_{2}$ binding energy, the intramolecular bond-length of O$_{2}$, and the excess charge on the adsorbed O$_{2}$ show even-odd alternations as a function of the number of gold atoms, correlating with the vertical electron detachment energy of Au$_ {n}$. The influence of pre-adsorbed H$_{2}$O on the O$_{2}$ adsorption is pronounced when the O$_{2}$ is adsorbed with an Au-O bond with the gold cluster and an O-H bond with pre- adsorbed H$_{2}$O, while the influence is relatively small for O$_{2}$ adsorbed with double Au-O bonds. Compared to the O$_{2} $ adsorption in the absence of H$_{2}$O, the binding energy of O$_{2}$ are increased by 0.4 eV, and the intramolecular bond- length are stretched by up to 0.03 \AA.