Theoretical Study of the O2 Interaction with a Tetrahedral Al4 Cluster

Employing both multireference configuration interaction (MRCI) and density functional theory (DFT) methods, we have studied the interaction of O2 with a tetrahedral Al4 cluster in the total spin triplet state. For a parallel to the base approach of O2 facing an apex of the pyramid, the O2 adsorption is hindered by a barrier. Both the MRCI and the DFT calculations show that after a small barrier, there are two local energy minima: a shallow one just above the apex atom and another deeper one below the apex atom. The latter corresponds to dissociative O2 adsorption. We discuss the implications of these findings for the understanding of O2 adsorption on defect sites of Al surfaces.