Binding energies of O2 and CO to small gold, silver, and binary silver-gold cluster anions from temperature dependent reaction kinetics measurements

A detailed analysis of experimentally obtained temperature-dependent gas-phase kinetic data for the oxygen and carbon monoxide adsorption on small anionic gold(Aun-, n = 1-3), silver(Aun-, n = 1-5), and binary silver-gold(AgnAum-, n + m = 2, 3)clusters is presented. The Lindemann energy transfer model in conjunction with statistical unimolecular reaction rate theory is employed to determine the bond dissociation energies E0 of the observed metal cluster complexes with O2 and CO. The accuracy limits of the obtained binding energies are evaluated by applying different transition-state models. The assumptions involved in the data evaluation procedure as well as possible sources of error are discussed. The thus-derived binding energies of O2 to pure silver and binary silver-gold cluster anions are generally in excellent agreement with previously reported theoretical values. In marked contrast, the binding energies of O2 and CO to Au2- and Au3- determined via temperature-dep endent reaction kinetics are consistently lower than the theoretically predicted values.