Fermi resonance coupling in the C–H stretching region of methoxide adsorbed on clean Ru(0 0 1): a combined RAIRS and theoretical study

A combined reflection–absorption infrared spectroscopy (RAIRS) and theoretical study on methoxide adsorbed on clean Ru(0 0 1) enabled to interpret the C–H stretching region of the spectrum. The Fermi resonance between the fundamental stretching modes and the overtones of the deformations has been analyzed. Density functional cluster model calculations (DFT) showed that methoxide adsorbs preferentially on hcp threefold cavities, and provided the unperturbed vibrational frequencies. Once corrected by the experimentally determined frequencies, they were used to calculate the Fermi resonance coupling constants by a normal mode model, assuming the local symmetry suggested by the experimental results (Cs). The present approach shows that a reliable description of the experimental C–H stretching region of adsorbed methoxide on Ru(0 0 1) may be obtained.