Theoretical study of stimulated desorption of protons from transition metal surfaces

The mechanism for near-threshold photon-stimulated desorption (PSD) and electron-stimulated desorption (ESD) is examined theoretically using finite cluster, quantum chemical techniques to model the interaction of a hydrogen atom with a metal surface. Configuration interaction calculations on clusters modeling both the <100> and <111> faces of an fcc crystal yield a consistent picture of the process. A band of strongly repulsive states which asymptotically dissociate to ions is found to lie approx.25 eV above the ground state. This excitation energy is consistent with the threshold observed in ESD and PSD experiments on the <100> surfaces of Ni and Pd. The states of this band all involve double excitations from the metal--hydrogen bonding orbitals