Adsorption And Dissociation Of O/O-2 On Flat And Stepped Palladium Surfaces

The 5-parameter Morse potential (5-MP) of an O-Pd system and the improved extended LEPS potential of an O-2-Pd system were constructed. The adsorption and dissociation of oxygen atoms and oxygen molecules on flat and stepped palladium single crystal surfaces were studied detailedly, and the data of adsorption sites, adsorption geometry, binding energy, eigenvibration, dissociative mechanism, etc. were obtained. Theoretical results show that the high-symmetry sites are the preferred adsorption sites for tilted adsorption of oxygen molecules, and the tilted angle depends on the number of atoms per unit surface area. Meanwhile, a variety of dissociation pathways are analyzed in detail related to the O-2-Pd(111) system. These results show that the adsorptive dissociation of oxygen molecules on the Pd(111) hollow site is precursor-mediated, on the Pd(111) bridge site is direct dissociation and on the Pd(111) top site is not only depended on the translational energy, but also depended on the vibrational energy. Moreover, the role of the step defect for oxygen atoms and oxygen molecules is also discussed related to flat surface. Theoretical results are in good agreement with the experimental results, and explain well the divergence [N. Salanov and V. N. Bibin, Surf. Sci. 441 (1999) 399; P. D. Nolan, B. R. Lutz, P. L. Tanaka and C. B. Mullins, Surf. Sci. 419 (1998) L107] related to the 02 dissociation mechanism.