INTERACTION OF NO WITH CLEAN AND K-DOSED RH(111) SURFACES .11. EELS AND PES STUDIES

The interaction of NO with clean and potassium covered Rh(111) surfaces has been investigated by means of EELS (in the electronic range), UPS and XPS. The appearance of the O 2p signal at 6.0 eV in UPS indicates the dissociation of NO at low coverage on the clean surface at 300 K. At high exposures the adsorption is preferentially molecular. In the presence of a potassium adlayer the thermal stability of adsorbed NO depended on the potassium coverage. At low K coverage the potassium promotes the dissociation due to enhanced back-donation from the d-orbitals of Rh into the 2π orbital of NO. At monolayer K coverage, the UPS and XPS spectra suggest an appreciable stabilization of NO; the dissociation started at 400-422 K. Above 422 K, the appearance of new photoemission signals at 4.0, 9.8 and 11.7 eV in UPS, and at 403.8 and 533.7 eV in XPS suggest the formation of NO2 species stabilized by potassium. This surface complex decomposes on Rh(111) at around 664 K. © 1990.