THE REACTIVITY OF MOLECULAR AND ATOMIC OXYGEN IN OXYGEN-EXCHANGE REACTION BETWEEN NO AND O-2 COADSORBED ON A PT(111) SURFACE

Surface reactions between (NO)-O-16 and O-18(2) coadsorbed on Pt(111) have been studied by temperature-programmed desorption (TPD), low ener gy electron diffraction and infrared reflection absorption spectroscop y (IRAS). When the surface covered with (NO)-O-16 and O-18(2) is annea led, (OO)-O-18-O-16 desorbs at 155 K and (NO)-O-18 at 145, 310, and 34 0 K. In addition, a new absorption line at 1658 cm(-1) due to (NO)-O-1 8 appears above 265 K. However, there is no indication of oxidation pr oducts of NO in the TPD and IRAS measurements. Thus, only oxygen-excha nge reactions take place on the coadsorbed surface. Reaction yields an d mechanisms of the oxygen-exchange strongly depend on the adsorption states of oxygen. At similar to 145 K, molecularly adsorbed oxygen and (NO)-O-16 (nu(NO) = similar to 1930 cm(-1)) directly interacting with the oxygen molecule are involved in the exchange reaction. Above 270 K the exchange reaction takes place between atop (NO)-O-16 (nu(NO) = s imilar to 1720 cm(-1)) and the metastable oxygen adatoms that do not p ossess a long-range order. On the contrary, the oxygen-exchange reacti on is greatly suppressed when NO is coadsorbed on the surface with wel l-ordered p(2X2)oxygen atoms. (C) 1995 American Institute of Physics.