Quantum steering effects in the dissociative adsorption of H-2 on Rh(100)

We show on the basis of ab initio local-density-functional calculations (with generalized gradient corrections) that the dissociative adsorption of a H-2 molecule on a Rh(100) surface is dominated by quantum-mechanical steering effects arising from the formation and modification of covalent metal-H bonds: As the molecule is lowered towards the surface, bond formation occurs first with the s, p(z), and d(3z2-r2) orbitals extending farthest from the surface. This attracts the molecule to the on-top position. Interaction with the t(2g) orbitals orients the axis of the molecule towards the bridge sites and drives the dissociation in a bridge-top-bridge configuration. Finally, bonding with the d(x2-y2) orbitals attracts the dissociated atoms to the fourfold hollows.