An ab initio electronic structure study of methyl adsorption and reaction on cluster models for the diamond surface

Electronic structure calculations were carried out for a series of hydrogen -terminated carbon clusters designed to model the 100- and 111-diamond surf aces, C-d(100) and Cd(111). The subjects of the calculations were: (1) meth yl radical (CH3.) adsorption on an activated diamond surface; and (2) hydro gen abstraction from adsorbed methyl via reaction with gas-phase atomic hyd rogen. The largest clusters were treated at the MP2/6-31G*//HF/6-31G*; leve l of theory. The results of higher level calculations on smaller clusters w ere used to estimate corrections to the MP2/6-31G*//HF/6-31G* energies. It is concluded that methyl adsorption is 6.8 kcal mol(-1) more exothermic on C-d(100) than on C-d(111). Also, the barrier for hydrogen abstraction from methyl adsorbed on C-d(100) is 2.4 kcal mol(-1) lower than that for abstrac tion from methyl adsorbed on the C-d(111) surface. Finally, the abstraction reaction energy is 0.8 kcal mol(-1) lower for methyl adsorbed on C-d(100) compared to methyl adsorbed on C-d(111). (C) 2000 Elsevier Science B.V. All rights reserved.