Coupled desorption and site conversion of co-adsorbates: A lattice gas analysis of thermal desorption and spectroscopic data of (NO+O)/Ru(001)

The (NO + O)/Ru(001) system constitutes a good example of complex desorptio n-site conversion with the advantage that the geometrical structures, the c overages, as well as detailed spectroscopic information on all participatin g species are available. We present a combined set of desorption data and v ibrational spectra with in situ determination of partial coverages in desor ption which show site-conversion for both increasing and decreasing tempera tures. This system is understood in detail by modeling the (NO + O) coadsor bate layer on Ru(001) as a lattice gas that accounts for the adsorbate stru cture and site-conversion, and explains the TPD spectra. The unusual featur es of the TPD spectra result in part from the dramatic coverage dependence of the sticking coefficient induced by site-exclusion. (C) 1999 Elsevier Sc ience B.V. All rights reserved.