Oxygen Species Adsorbed on Oxides: Part 1.—Formation and Reactivity of (O_)s on MgO

Abstract

Nitrons oxide reacts with F*(H) centres (surface oxygen ion vacancies with a single trapped electron) to give (O-)/' ions adsorbed at the anion vacancy. The reaction, FS+(H)+N2O ->(O_)t± + N2 is quantitative and the reflectance spectrum indicates a band centred at 2 eV which is ascribed to the (O~)+ centre. Comparison of the optical transition energy calculated from the e.s.r. data with the observed transition shows that the normally accepted value of 135 cm’1 for the spin-orbit coupling of the O_ ion is too low and that a value of >200 cm-1 is more appropriate for the solidstate. Nitrous oxide also reacts with other surface centres to give an adsorbed species which may be (O2_)s or (O2)s- The reaction of (O_)s+ with hydrogen reforms the FS+(H) centre which then reacts with more nitrous oxide; the react ion can be cycled several times. The reactions of (O-)+ with O2, CO2, alcohols and olefins are also investigated. To facilitate reference to various types of surface defects and adsorbed species a nomenclature is proposed which is compatible with a recently suggested notation for defects in bulk lattice.