MULTIMETHOD STUDY OF THE ADSORPTION OF NO ON RU(001) .1. XPS, UPS AND XAES MEASUREMENTS

The adsorption of NO on the basal plane of ruthenium at temperatures between 80 and 700 K has been investigated using XPS, UPS and XAES. The combination of these spectroscopies allows the differentiation of molecular and dissociated states and the in situ analysis of their quantitative evolution with exposure at various temperatures and with heating. The main results are: Below ∼200 K, NO adsorbs on Ru(001) in two different molecular states termed v1 and v2; their relative quantities depend on the adsorption temperature. At adsorption temperatures above 200 K, a dissociative ß-state is formed first, followed by molecular adsorption into v1 and/or v2. Heating of low temperature layers shows that in diluted layers dissociation starts again at ∼200 K without desorption, while from saturated layers NO must be desorbed to make dissociation possible, due to spatial requirements. Around 450 K all molecular NO is removed; all N atoms have left the surface by ∼600 K, leaving behind only O atoms. Arguing from the measured binding energies and other spectral features, and by comparison with published ELS data, v1 and v2 are assigned to bridge-bonded and linearly bound NO. © 1979.