Vibrational spectrum of methoxy adsorbed on metal surfaces: ab initio calculations and experiments

Ab initio electronic structure calculations are used to assign the vibrational spectra of methoxy adsorbed on Mo(110). Methoxy with two different orientations with respect to the surface, perpendicular (C-3v) and tilted (C-s), were investigated. Using calculations on Mo-methoxy and Rh-methoxy complexes to represent different orientations and symmetries, it is shown that experimentally observed changes in spectra associated with reorientation and isotopic substitution (CH3O-, CHD2O- and CD3O-) are reproduced completely by the calculations. Problems with the use of vibrational data on gas-phase species for interpreting surface data are presented. Limitations in the approach associated with Fermi resonances are discussed. (C) 1997 Elsevier Science B.V.