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An Ab Initio Electronic Structure Study of Methyl Adsorption and Reaction on Cluster Models for the Diamond Surface

Brown, R. C.; Cramer, C. J.; Roberts, J. T.
Diamond Relat. Mat. 2001, 10, 39

Electronic structure calculations were carried out for a series of hydrogen-terminated carbon clusters designed to model the 100- and 111-diamond surfaces, C-d(100) and C-d(111). The subjects of the calculations were: (1) methyl radical (CH3.) adsorption on an activated diamond surface; and (2) hydrogen abstraction from adsorbed methyl via reaction with gas-phase atomic hydrogen. The largest clusters were treated at the MP2/6-31G*//HF/6-31G* level of theory. The results of higher level calculations on smaller clusters were 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 abstraction 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).

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