Activation energy and mechanism of CO desorption from (100) diamond surface

Abstract

An apparent activation energy for CO desorption from (100) diamond surfaces exposed to atomic oxygen was determined by thermal desorption spectroscopy 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 β-scission of the C—CO bond, formation of a dimer C—C bond, and finally cleavage of the second 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 agreement with the experimental activation energy. Taken together, the broad experimental desorption-peak feature and the multitude of possible desorption sites with differing potential-energy barriers, suggests the existence of a distribution of CO sites on diamond surfaces.