FTIR overtone spectroscopy on surfaces. The C—O mode in chemisorbed methoxy on Ni(111)

We report the observation of vibrational overtone for an adsorbate on a single crystal surface by high-resolution vibrational spectroscopy. A very weak absorption band at 2017 cm−1 is identified as the first overtone of the C—O stretching fundamental (at 1027 cm−1 of CH3O-Ni(111). The anharmonic shift in the absence of dipole coupling and mechanical renormalization is determined to be 8.5±2 cm−1, slightly smaller than that of the C—O stretching vibration in methanol, 12.5 cm−1. Surprisingly no C—O bond weakening is found in CH3O-Ni(111) compared to gas-phase methanol.