Cycloaddition reactions of unsaturated hydrocarbons on the Si(100)-(2×1) surface: theoretical predictions

Abstract

First-principles electronic structure calculations have been used to study the structure, energetics and vibrational spectra of the chemisorption products of several unsaturated hydrocarbons on the Si(100)-(2×1) surface. The calculations use a hybrid non-local density functional theory and a cluster model of the surface. Ethylene and acetylene react by a [2s+2s] cycloaddition mechanism. Conjugated dienes (1,3-cyclohexadiene, 1,3-butadiene, 2,3-dimethyl-1,3-butadiene) and benzene can also react by a novel [4s+2s] cycloaddition, or Diels–Alder mechanism. For each diene, the Diels–Alder product is energetically favored over the more strained [2s+2s] product. The reaction mechanism for Diels–Alder addition, other competing reactions, and the effects of post-hydrogenation are all discussed. Comparisons to experimental observations are made throughout.