An infrared vibrational spectroscopic study of the interaction of methanol with oxygen-covered Cu(111)

Reflection-absorption infrared spectroscopy has been used to characterise further the formation of the surface methoxy species, CH3O-, on Cu(1 1 1) through the interaction with pre-adsorbed oxygen. Using a simple titration experiment, the relative reaction probability at 300 K has been determined as a function of oxygen pre-coverage. The experiments show a low oxygen coverage of approximately 0.04 ML or less to produce the most reaction at this temperature, although higher coverages appear to be favoured at lower reaction temperatures. The results support the earlier suggestion of Russell et al. [Surf. Sci. 163 (1985) 516] that the reaction occurs at 'perimeter sites' but also indicate the existence of a transiently adsorbed methanol precursor state on the clean surface. Coverage-dependent shifts in the C-O stretching frequency are shown to be attributable almost entirely to dynamic dipole coupling, with at most very small contributions from chemical shifts due to co-adsorbed oxygen or changing methoxy coverage, although chemical shifts may contribute in the C-H-related vibrational modes. (C) 2002 Published by Elsevier Science B.V.