Theoretical Study on the Interaction between Xenon and Positively Charged Silver Clusters in Gas Phase and on the (001) Chabazite Surface

A systematic study on the adsorption of xenon on silver clusters in the gas phase and on the (001) surface of silver-exchanged chabazite is reported. Density functional theory at the B3LYP level with the cluster model was employed. The results indicate that the dominant part of the binding is the a donation, which is the charge transfer front the 5p orbital of Xe to the 5s orbital of Ag and is not the previously suggested d(pi)-d(pi) back-donation. A correlation between the binding energy and the degree of a donation is found. Xenon was found to bind strongly to silver cluster cations and not to neutral ones. The binding strength decreases as the Cluster size increases for both cases, clusters in the gas-phase and on the chabazite surface. The Ag+ cation is the strongest binding site for xenon both in gas phase and on the chabazite surface with the binding energies of 73.9 and 14.5 kJ/mol, respectively. The results also suggest that the smaller silver clusters contribute to the negative chemical shifts observed in the Xe-129 NMR spectra in experiments.