Identification of oxygen species adsorbed on reduced titanium dioxide

The nature of oxygen adsorbed on slightly reduced TiO2 has been investigated using oxygen enriched with 17O2. On anatase, the oxygen adsorbs as O–2 with a hyperfine splitting Axx about g3 of 77 G; no structure could be resolved for Ayy and Azz. On rutile, oxygen adsorbs as O–2 on two sites of different thermal stability; (I) with g1= 2.030, g2= 2.008, g3= 2.004 and Axx= 76 G, and (II) with g1= 2.020, g2= 2.009, g3= 2.003 and Axx= 72 G. The evidence indicates that O–2 exists in a largely ionic form on TiO2 and other oxides. A symmetrical line at g= 2.003 which appears on some anatase samples after oxygen adsorption is attributed to the localization of a conduction electron by the adsorbed oxygen.