Density functional study of hydrogen binding on gold and silver-gold clusters.

A theoretical study was carried out on the binding of hydrogen on small bimetallic Ag(m)Au(n) (m + n < or = 5) and pure Au(n) (n < or = 5) clusters with neutral, negative, and positive charge state. It is found that the composition and charge state of clusters have strong influence on the most favorable binding site. The adiabatic ionization potentials, electron affinities, and hydrogen binding energies of cluster hydrides increase with the Au content increasing for the given cluster size. The cationic silver-gold cluster hydrides prefer ejection of Au-containing products whereas the anionic silver-gold cluster hydrides prefer ejection of Ag-containing products. The magnitude of metal-H frequency in combination with the metal-H bond length indicates that, with the same type of the binding site, the Au-H interaction is stronger than the Ag-H interaction.