Ab initio cluster model approach to the chemisorption of hydrogen on mercury

Abstract

The interaction of atomic hydrogen with a cluster model (Hg 7) simulating the mercury surface has been carried out at the ab initio SCF level using non-empirical pseudo-potentials and moderately large basis sets. Two different sets of pseudo-potentials were used dealing explicitly with twelve and two valence electrons, respectively. In the first set, all the cluster atoms are treated as twelve-electron atoms and in the second one only the mercury atom interacting directly with atomic hydrogen carries explicitly its d electrons. Two different electronic states being of different physical nature were studied. Thus, the neutral ground state is 2A 1 dissociating into neutral fragments. However, an ionic 2B 1 electronic state dissociating into Hg + 7 +H - was found to present a minimum lying very close in energy to the minimum of the neutral electronic ground state. The mixed approach is accurate enough to deal with the electronic ground state but not with the ionic state, due to the lack of d-shell repolarization induced by the charge transfer.