Resonance ionization detection of neutral 0(²Pj) produced from stimulated surface processes

We report the first quantum-state specific detection of ground-state atomic oxygen 0(³P) above an electron irradiated adsorbate-covered surface using laser resonance-enhanced multiphoton ionization spectroscopy. Electron-stimulated desorption of O(3P., is not observed from an O-covered Pt(111) surface, but 0(³P) fragments are produced from electron-stimulated dissociation of NO₂(fl) coadsorbed with O (#_o=0.75 ML) on Pt(111). The 9-10 eV threshold for O(³P,) formation correlates with that observed for NO₂(fl) dissociation. The measured OCPj) spin-orbit state distribution is (5.0):(2.5): (1.0) for.1 1, and 0, respectively. This is within experimental error of the 2./ + 1 statistical (T— oo) limit. No gas phase OCPj) is detected from the stimulated dissociation of adsorbed O₂ on Pt (111); however, we have utilized the O (\\\\\\\\P,) detection capability as an indirect probe of NO₂ production from an electron-stimulatedsurface reaction between coadsorbed O₂ and NO on Pt (The NO₂ is detected by laser photolysis above the surface. The — 10-eV NO₂ production threshold correlates with dissociative ionization from the 3a_gmolecularbonding orbital of O₂{a). Dissociative ionization can produce energetic O atoms which may then react with a coadsorbed NO, producing an NO₂ desorbate.