THE ADSORPTION OF NITRIC-OXIDE ON AN OXYGEN COVERED PD(100) SURFACE

The adsorption of nitric oxide on an oxygen-precovered Pd(100) surface has been studied using high-resolution electron energy loss spectroscopy (EELS) and low-energy electron diffraction (LEED). The vibrational properties of the nitric oxide molecules adsorbed on the Pd(100)p(2 x 2)O surface are only marginally changed compared with adsorption on the clean Pd(100) surface. The p(2 x 2)O structure is, however, influenced by the presence of nitric oxide on the surface. For temperatures where oxygen diffusion is possible the adsorbates tend to segregate and as a consequence the p(2 x 2)O is compressed locally to higher densities then 0.25 monolayers approaching a c(2 x 2) structure. For a particular nitric oxide dose and substrate temperature it is possible to isolate a new oxygen species, assigned to oxygen adsorbed in the bridge position in contrast to the p(2 x 2)O and c(2 x 2)O structures where the oxygen atom is adsorbed in the hollow position.