Resonance ionization detection of neutral O(3PJ) produced from stimulated surface processes

Abstract

We report the first quantum‐state specific detection of ground‐state atomic oxygen O(3PJ ) above an electron irradiated adsorbate‐covered surface using laser resonance‐enhanced multiphoton ionization spectroscopy. Electron‐stimulated desorption of O(3PJ ) is not observed from an O‐covered Pt(111) surface, but O(3PJ ) fragments are produced from electron‐stimulated dissociation of NO2(a) coadsorbed with O (θ0=0.75 ML) on Pt(111). The ∼9–10 eV threshold for O(3PJ ) formation correlates with that observed for NO2(a) dissociation. The measured O(3PJ ) spin‐orbit state distribution is (5.0):(2.5):(1.0) for J=2, 1, and 0, respectively. This is within experimental error of the 2J+1 statistical (T→∞) limit. No gas phase O(3PJ ) is detected from the stimulated dissociation of adsorbed O2 on Pt(111); however, we have utilized the O(3PJ) detection capability as an indirect probe of NO2 production from an electron‐stimulated surface reaction between coadsorbed O2 and NO on Pt(111). The NO2 is detected by laser photolysis above the surface. The ∼10‐eV NO2 production threshold correlates with dissociative ionization from the 3σg molecular bonding orbital of O2(a). Dissociative ionization can produce energetic O atoms which may then react with a coadsorbed NO, producing an NO2 desorbate.