Characterization and Reactivity of the Mo4S6+Cluster Deposited on Au(111)

Abstract

Mass-selected cluster deposition was used to investigate the chemical and thermal properties of the Mo 4S 6 cluster deposited onto a Au(111) substrate. Auger spectroscopy and (13)CO thermal desorption measurements demonstrate that the clusters behave independently up to coverages of ∼0.15 ML, while at higher coverages, cluster crowding or island formation results in no net increase in Mo-atom adsorption sites. DFT calculations show that CO binding on the Mo-atom top site is strongly preferred over the side sites, with scaled binding energies in reasonable agreement with the experimentally derived binding energy of 0.7 eV. DFT calculations predict that the total adsorption energy for sequential addition of two CO molecules (top and side site) is nearly additive, whereas the addition of a third CO to another empty Mo side site is less stable. The latter is attributed to repulsive intercluster interactions and is consistent with the experimentally estimated sticking coefficient of 0.4 ± 0.1. In contrast to C...