AN AB-INITIO STUDY OF HYDROGEN ABSTRACTION FROM CLUSTER-MODELS FOR THE DIAMOND SURFACE

Electronic structure calculations have been performed on hydrogen-term inated carbon clusters. Optimized geometries of increasingly larger cl usters were examined in order to obtain clusters that accurately model the 111 and 100 diamond surfaces. The clusters were used to character ize the energetics and transition-state structures for hydrogen abstra ction by atomic hydrogen from the two surfaces. For the larger cluster s, calculations at the MP2/6-31G//HF/6-31G* level of theory were perf ormed, and these were corrected on the basis of calculations using hig her levels of theory applied to representative smaller clusters. It wa s determined that the barrier to H-atom abstraction from the 100 surfa ce was 2-3 kcal.mol(-1) higher than that from the 111 surface. The rea ction energy for abstraction was also found to be higher from the 100 surface than from the 111 surface, by 3-5 kcal.mol(-1).