Photophysics and Photochemistry of NO on Ag(111), Cu(111), and Si(111)7 × 7

Abstract

We have performed photon induced desorption (PID) from NO adsorbed on Ag(111), Cu(111), and Si(111)7 × 7 at 85 K 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 these surfaces and subsequent changes after irradiation were characterized by high resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). On Ag(111), PID of NO and N₂O have been observed from the NO saturated surface. On Cu(111), PID of both NO and N₂O has also been observed. N₂O is photosynthe-sized from photoinduced reactions. On Si(111)7 × 7, photon irradiation induces both desorption and dissociation of NO and photosynthesis of N₂O. The N₂O products partially desorb intact and partially dissociate into N₂ and O, which leads to N₂ desorption. PID of NO on Ag(111) and Cu(111) is state selective and occurs primarily for NO adsorbed in atop states. On Si(111)7 × 7, both atop and bridge bonded NO are photoactive. From the wavelength dependences of the PID, we suggest that the photoexcitation of the adsorbate (2π_occ level) is the more important mechanism for Ag and Cu for photon energy≥3.4 eV; the substrate mediated process, however, is more dominant for Si.