The influence of adjacent molecular groups on the adsorption of H., CH₃., CH₂., C₂{H}.$, and ${C}₂H₂ on the diamond (111) surface has been investigated theoretically. Ab initio molecular-orbital theory was used in order to calculate the adsorption energies of these different species. The adsorption energies were found to be in the order C₂{H}.$>${H}.$>${CH}₂.$>${CH}₃.$>${C}₂H₂ (onefold adsorption) for all the different types of neighboring environments investigated. The adsorbed species are here either surrounded by only H. atoms or one of these H. atoms is being removed, leaving a diradical site, or replaced by a CH₂. or CH₃. species, respectively. Generally, the sterically hindering effects of the branched neighboring species CH₂. and CH₃. will decrease the adsorption energy by about 60 and 100 kJ/mol, respectively. An exception is the C₂{H}₂$ species adjacent to a ${CH}₂.$ group, where the presence of the ${CH}₂.$ group increases the adsorption energy, due to a C-C bonding interaction between the two adsorbed species. This implies that ${C}₂H₂ adsorption under these circumstances will be energetically competitive with CH₃. adsorption.
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Larsson et al. (1995) studied this question.
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