Luminescence during oxygen adsorption on thorium oxide

Some novel features concerning the light emitted during oxygen adsorption on thorium oxide surfaces are presented and discussed. The variation of light intensity with time reveals the existence, after the initial peak, of a secondary maximum depending on the conditions of the previous surface treatment with hydrogen. Carbon monoxide added to the oxygen causes this secondary maximum to vanish. Finally, the spectrum of emitted light consists, in the visible region, of a broad structureless band, between 500 and 800 nm. These findings are interpreted as due to the possible occurence of two radiative transitions between adsorbed species: (I) Osub(2ads)+e-→Osub(2ads)sup(-); (II) Osub(ads)+e-→Osub(ads)sup(-). (author)