ACTIVATION-ENERGY AND MECHANISM OF CO DESORPTION FROM (100) DIAMOND SURFACE

An apparent activation energy for CO desorption from (100) diamond sur faces exposed to atomic oxygen was determined by thermal desorption sp ectroscopy performed in ultrahigh vacuum and found to be equal to 45.0 kcal/mol. A minimum potential-energy reaction path was identified by semiempirical quantum chemical calculations. Starting with an O-on-top radical site, the reaction proceeds through a beta-scission of the C- CO bond, formation of a dimer C-C bond, and finally cleavage of the se cond C-CO bond. The largest barrier along this pathway is that of the final desorption step; it is equal to 38.4 kcal/mol, in reasonable agr eement with the experimental activation energy. Taken together, the br oad experimental desorption-peak feature and the multitude of possible desorption sites with differing potential-energy barriers, suggests t he existence of a distribution of CO sites on diamond surfaces.