Oxygen species adsorbed on oxides. Part 2.—Formation of (O –3)s on MgO

Abstract

A MgO surface containing adsorbed (O^–)⁺_s ions reacts with excess oxygen to form the molecular ion (O^–₃)_s. This ion has been characterized by e.s.r. using oxygen enriched with ¹⁷O and shows a complex hyperfine structure. Heating at 400 K converts the (O^–₃)_s ions to (O^–₂)_s and an isotopic exchange occurs between the various oxygen nuclei. The optical data indicate that a band close to 420 nm is associated with the (O^–₃)_s species. Calculations using electron affinity and bond energy data indicate that the reaction O^–+ O₂→ O^–₃ is exothermic and that (O^–₃)_s must be considered as a possible adsorbed oxygen species on oxides.