Oxygen and silver clusters: transition from chemisorption to oxidation.

We use the adsorption probabilities of molecular nitrogen and oxygen to study the physi- and chemisorption on small silver particles. The physisorption of nitrogen is governed by the structure of the particle surface. The sticking of oxygen additionally involves the electronic configuration of the metal cluster. At 77 K molecular oxygen sticks chemisorbed to the particles with a transfer of one electron. At temperatures above 105 K the chemisorption transforms into oxidation, invoking the dissociation of the oxygen molecule and the loss of a single oxygen atom.