A comparison of the on-top dissociation of H2 on Ni(100) and Cu(100)

The on-top dissociations of H₂ on Ni(100) and Cu(100) are studied using a cluster approach. Correlation effects are accounted for through the use of CASSCF and CCI methods. The central metal atom is treated with all its electrons whereas the other cluster atoms are described by recently developed one electron ECP's. A molecular chemisorbed H₂ state on nickel, similar to that recently observed experimentally, was identified in the cluster calculations and also for the triatomic NiH₂. No such state was found on copper. The large differences found for the on top dissociation of H₂ on nickel and copper are attributed solely to the difference in 3d orbital occupation. The parallel between the on top dissociation reaction on the cluster and the dissociation on a single atom is also studied. While the neutral triatomic NiH₂ represents a qualitatively correct model in the nickel case, the negatively charged CuH ₂ ^– is required as a model in the copper case.