Cycloaddition reactions of unsaturated hydrocarbons on the Si(100)-(2x1) surface: theoretical predictions

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 x 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 [2(s)+2(s)] cycloaddition mechanism. Conjugated dienes (1,3-cyclohexadiene, 1,3-butadiene, 2,3-dimethyl-1,3-butadiene) and benzene can also react by a novel [4(s)+2(s)] cycloaddition, or Diels-Alder mechanism. For each diene, the Diels-Alder product is energetically favored over the more strained [2(s) +2(s)] 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. (C) 1998 Published by Elsevier Science B.V. All rights reserved.