Symmetry and orientation ofCH3O on Cu(100)

The C-H stretch vibrational modes of ${\mathrm{CH}}_3$O chemisorbed on a Cu(100) surface have been studied using infrared spectroscopy. Three absorption peaks were found indicating that the symmetry of the ${\mathrm{CH}}_3$ group is broken. Comparison with the infrared spectra of free methanol shows that the ${\mathrm{CH}}_3$O group is rather little perturbed by the chemisorption and that the molecules definitely are tilted on the surface. Thermal desorption spectra indicate that the dehydrogenation of ${\mathrm{CH}}_3$O to ${\mathrm{H}}_2$CO goes via the adsorption of a hydrogen atom on the copper surface during a low frequency bending mode.