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The interaction of CO molecules with the surface of Sc, Y, and La oxides leads to the formation of paramagnetic polyatomic surface compounds containing two equivalent carbon atoms and lattice cations; a structure for the adsorbed (CO)2.radical anions which explains their high thermal stability and reactivity has been suggested.The nature of intermediate surface compounds is important in elucidating the mechanism of catalytic reactions involving CO. A large number of variations of the forms of adsorbed CO have been found on oxide catalysts of a basic type. In addition to the usual carbonyl and carbonate-carboxylate structures, surface ionic compounds containing two and more adsorbate molecules have been formed. They were detected on Mg01J and rare earth oxides3.4 by optical and e.s.r. spectroscopy. With rare earth oxides (-20% of m ~n o l a y e r ) ~ the maximum chemisorption of CO as dimers (compared with that on monometallic oxides) was attained.3,4The aim of the present work was to establish the structure of the surface compounds which are formed during the interaction of CO with rare earth oxides by e.s.r. methods using W O and D20. The e.s.r. spectra were obtained on a Jeol JES-3BS-Q radiospectrometer in X and Q bands.The Sc, Y, and La oxides evacuated at 800-1100 K gave signals with g = 2.003 (Figure 1, signal A) when CO was admitted at 230-620 K. The spectra of radical A on scandium, yttrium, and lanthanum oxides possessed different

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