Evidence of repulsive interactions between NO, O, and N on Ir(110). A fastx-ray photoelectron spectroscopy study

The adsorption of NO on Ir(110) was studied in the temperature range from 2 00 to 500 K with fast x-ray photoelectron spectroscopy (XPS) using synchrot ron radiation. Only three surface species were observed: molecular NO, atom ic O, and atomic N. NO dissociation starts at temperatures higher than 300 K and molecular NO can coadsorb with O-ads in the whole temperature region studied. By collecting O 1s and N 1s spectra within a few seconds we obtain ed information on the interaction between N-ads, O-ads, and NOads with incr easing coadsorbate coverage. The N-ads-O-ads interaction has been found to be strongly repulsive. As a consequence, the N-ads is destabilized already at moderate coverages and temperatures above 350 K leading to the removal o f N-ads from the surface in the form of N-2 desorption. (C) 2000 American I nstitute of Physics. [S0021-9606(00)70547-2].