Physisorption of deuterium on deuterated nickel clusters

The physisorption of deuterium molecules on small nickel clusters having chemisorbed deuterium atoms is identified. The principal evidence for physisorption is the appearance at reaction temperatures below 200 K of product species having more deuterium bound to them than the chemisorption maximum, and a lowering of cluster ionization potentials (IPs) for these species. It is argued that the IP lowering is a consequence of molecular physisorption, and that identification of the number of physisorption sites on cluster surfaces can be used to infer structural information.