Competing Reactions of Vinyl and Hydroxyl Groups of Vinyl Alcohol on Ge(100): Effects of Vinyl Substituent on Dissociative Adsorption

We investigated the adsorption of vinyl alcohol onto Ge(100) surface by performing density functional theory calculations. The C-O dissociative adsorption of vinyl alcohol produces two fragments, a hydroxyl group and a vinyl group, each of which bonds with a different germanium atom. The dissociated vinyl and hydroxyl groups passivate the dangling bonds of surface germanium atoms to form the most stable configurations containing HO-Ge-Ge-CH=CH₂ linkages. The reactions of the C=C bond of the vinyl group can generate enantiomer products with characteristic stereochemistry. The cycloaddition of the vinyl group is not favored thermodynamically, although paired adsorption at an adjacent site can stabilize cycloaddition structures. Our kinetic study reveals that the C-O dissociative adsorption has a larger activation barrier than O-H dissociative adsorption, although the transition state energy is close to that of the reactants. According to our analysis of the kinetics and thermodynamics of this system, the C-O dissociative adsorption, which produces an unreacted vinyl group perpendicular to the germanium surface, is a major reaction at room temperature. Our simulated images of the stable adsorption structures show the characteristic electronic density features of the functional groups.