The surface-radical-surface-olefin recombination step for CVD growth of diamond. Calculation of the rate constant from first principles

Recombination of a surface-radical with a surface-olefin (SR-SOR) to form a six-membered ring is a critical step in the current mechanism for chemical vapor deposition growth of the diamond (100) surface. We estimate the rate constant for SR-SOR by combining quantum chemistry calculations, molecular mechanics calculations, and transition state theory. The ab initio calculations include extensive electron correlation (MP2 and GVB ^* SD CI) on cluster models which were corrected for steric interactions of the cluster with the rest of the surface and for stran effects on the lattice. The ab initio vibrational frequencies, which were used to construct a partition function for calculating the entropy, were calculated at the MP2 level. Transition state theory was used to obtain the rate constant, k = 5.6 x 10¹² e ^{-8800 RT} s^-1. This implies that under normal growth conditions SR-SOR is fast compared to competing gas-surface reactions.