Role of the surface site in the kinetics of H atom association with diamond surfaces

The reaction path Hamiltonian model and the MAPS/HDIAM analytic potential energy function were used in a canonical variational transition state theory (CVTST) study of H atom association with diamond surfaces. CVTST rate constants are compared for H atom association with a terrace site on the diamond {111} surface and two ledge sites on this surface. The CVTST association rate constant is largest for the terrace site and is 3.9 and 2.4 times larger than the rate constant for one of the ledge sites at 300 and 2000 K, respectively. Nonbonded interactions between the associating H atom and surface H atoms decrease the attractiveness and increase the repulsiveness of the radial and angular potentials, respectively, along the association reaction path. The CVTST rate constants are found to be in good agreement with classical trajectory rate constants, also calculated for the MAPS/HDIAM potential. This study shows how nonbonded interactions and steric effects may affect rate constants for diamond surfaces.