| Abstract
| - Density functional calculations have been performed on possible mechanisms for the hypothetic C−H bondcleavage process of benzene chemisorbed on the Si(100) surface, in order to shed light on the analogousprocess on larger polycyclic aromatic hydrocarbons. We first identified the minima on the potential energysurface for the benzene adsorption on Si(100) and for the breaking of two C−H bonds, with formation of twoSi−H bonds, and then we analyzed possible pathways for the C−H bond cleavage, looking for the transitionstates connecting the adsorption configurations to the final products of C−H breaking. We identified twoadsorbed configurations of benzene from which the breaking of two C−H bonds can be accessible, i.e., the1,2 tilted di-σ bonded configuration on top of a single dimer (T) and the 1,4 di-σ bonded configuration wherebenzene bridges two dimer rows (BR). The kinetically most favorable reactive channel on the T configurationinvolves the abstraction of two hydrogen atoms on the sp3 carbon atoms by the silicon atoms of an adjacentdimer, with an energy barrier of 22.0 kcal mol-1. Although seemingly low, such an activation energy is notexpected to be accessible at temperatures below the onset of benzene desorption from this configuration,which requires 15.9 kcal mol-1. The kinetically most favorable reactive channel on the BR configuration,which has not been experimentally detected for the benzene molecule, involves the rupture of one Si−Cbond, passing through an energy barrier of 29.8 kcal mol-1, and ends with the formation of a Si−H bond anda vertical phenyl unit anchored on a silicon dimer.
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