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 σ_NO = 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 2π_occ level). At low photon energies (hv < 4 eV), the adsorbate (2π_occ 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.