Adsorption of methanol, formaldehyde and formic acid on the Si(100)-2x1 surface: A computational study

The adsorption of methanol, formaldehyde and formic acid on the Si(100)-2x1 surface have been investigated by means of first-principles density functi onal cluster model calculations and ab initio ONIOM calculations. The disso ciative adsorption of methanol on the Si(100) surface takes place readily, giving rise to Si-OCH3 and Si-H surface species. The reaction, occurring ba rrierlessly via a stable chemisorbed state and the transition state for dis sociation, is highly exothermic. The chemisorption of formaldehyde on the S i(100) surface is also barrierless and exothermic with the formation of a 4 -member ring -SiCOSi- surface species. This result indicates that the carbo nyl (C=O) group can undergo cycloaddition onto the Si dimer on the Si(100) surface. The dissociative chemisorption of formic acid occurs readily on th e Si(100) surface with the formation of unidentate formate surface species and H adatoms. Its exothermicity is higher than 60 kcal mol(-1). The vibrat ional frequencies of the surface species produced by the chemisorption of t he three C-1 molecules have been calculated and compared with the available experimental data.