NO adsorption on the Rh(110) surface: kinetics and composition of the adlayer studied by fast XPS

The adsorption and dissociation of NO on the Rh(110) surface were studied by synchrotron radiation X-ray photoemission spectroscopy at temperatures in the range 210-370 K. The O Is or N Is spectra were collected every 14 s while the surface was continuously exposed to a steady NO gas pressure. The difference in the binding: energies for the atomic oxygen (O Is less than or equal to 530.2 eV), atomic nitrogen (N Is similar to 397.2 eV) and molecular upright bonded NO molecules (O Is greater than or equal to 531.0 eV and N Is similar to 400 eV) allowed us to distinguish these surface species and to follow the evolution of the adsorbate layer. In addition to these dominating surface species a new species, characterized by O Is binding energy of 530.7 eV and N Is binding energy similar to that of the atomic nitrogen, was detected within a narrow coverage range. This state is tentatively assigned to a "lying down" NO bonding configuration, detectable at the timescale of the measurements. The uptake plots, constructed using the integrated intensity of the deconvoluted O Is and N Is spectra, are used to elucidate the effect of the reaction temperature and surface coverage and composition on the kinetics of dissociative and molecular NO adsorption of Rh(110). (C) 1998 Elsevier Science B.V. All rights reserved.