PHOTODESORPTION OF NO ON AG(111) AT 80-K

We have performed photon induced desorption (PID) from NO adsorbed on Ag(111) in the wavelength region 250-800 nm by using Xe and Hg-Xe arc lamps in combination with a monochromator (P ≤ 30 mWcm-2). The adsorption of NO on Ag(111) and subsequent changes after irradiation were characterized by high resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). PID of NO and N2O have been observed from the NO saturated surface. PID takes place with a high cross-section only from species adsorbed in atop states and the cross-section increases strongly with the photon energy. At λ = 280 nm (4.4 eV), the cross-section for NO desorption is σNO = 5.5 × 10- 18 cm2. The PID mechanisms of NO on Ag(111) are discussed in terms of the photoexcitations of the substrate (Ag 5s and 4d level) and the adsorbate (NO 2πocc level). At low photon energies (hv < 4 eV), the adsorbate (2πocc level) and substrate (5s level) photoexcitations are the driving mechanisms while at higher photon energies (above Ag 4d level excitation), the d level excitation is also possible. Both adsorbate and substrate photoexcitations can lead to desorption. © 1990 Pergamon Press plc.