Adsorption dynamics of CO on Pd(1 1 0): energy dependence, structure insensitivity and the role of the surface electronic structure

The translational energy (ET) dependence of CO chemisorption has been investigated on Pd(1 1 0). A steep increase from 0.61 to 0.93 is observed in the initial sticking probability S0 with increasing ET from 27 to 93 meV. Comparison to density functional theory calculations suggests a steering-mediated adsorption channel, driving slow molecules towards less favorable surface sites. This long-range interaction between CO and the Pd d-orbitals screens the potential influence of the surface structural corrugations on the CO adsorption and thus provides an explanation to the well-known structure insensitivity of CO adsorption on Pd surfaces. For ET>93 meV the adsorption reverts back to the direct chemisorption mechanism found on other Group VIII metals.