Molecularly chemisorbed intermediate state to oxygen adsorption on Pd{110}

Translational energy (ET) dependence of oxygen (O-2) adsorption on Pd{110} has been investigated with molecular beam surface scattering (MBSS) experiments. The initial sticking probability (So) and adsorption kinetics of oxygen are shown to depend strongly on E-T of the incident molecule. An inverse surface temperature dependence of So is also observed at low translational energies. Using density-functional theory calculations several O-2 adsorption potential energy curves (PECs) on Pd{110} were determined. Direct adsorption PECs with an activation barrier and two PECs with a molecular chernisorption state were found. Both experimental and theoretical results indicate a twofold adsorption mechanism. At low ET molecules end up in a very attractive molecularly chemisorbed precursor state from which they eventually dissociate. At higher ET more molecules begin to dissociate via a direct activated adsorption channel. (C) 2003 Elsevier B.V. All rights reserved.