ELEMENTARY REACTION-MECHANISM OF DIAMOND GROWTH FROM ACETYLENE

Kinetically and thermodynamically plausible reactions that can explain the growth of diamond from acetylene are introduced. This class of reactions includes the addition of acetylene to a biradical with at least one of its sites being either a (100)-(2X1) dimer carbon or a secondary carbon, so that the admolecule can undergo a series of H-additions, H-abstractions, and beta-scissions leading to incorporation of its carbon atoms into a diamond lattice. Several examples are presented and supported with the results of semiempirical quantum-chemical and transition-state-theory calculations. Among those considered, the most favorable reaction pathway is initiated by the addition of an acetylene molecule that forms a bridge between adjacent dimer rows.