INTERACTION OF METHANOL WITH A POLYCRYSTALLINE PLATINUM SURFACE STUDIED BY INFRARED REFLECTION ABSORPTION-SPECTROSCOPY

The chemistry of methanol on polycrystalline platinum resembles that on a Pt(111) surface. The amount of thermal decomposition to CO and H2 saturates for low-temperature exposures higher than 0.5 Langmuir. The first monolayer is filled upon an 1.3 L exposure. Photoelastic modulated infrared spectra allow, for the first time, the measurement of the IR absorption bands associated with both hydroxyl and methyl stretchings of CH3OH and CD3OD at submonolayer level. The delayed appearance of the hydroxyl IR band upon exposure at 90 K and the simultaneous detection of both symmetric and asymmetric stretching modes of the methyl group indicate that the CH3 group axis is inclined with respect to the surface normal and that the OH group axis is quasi parallel to the surface plane at the submonolayer level. Crystallization of the adsorbate could be achieved for coverages higher than 3 monolayers. These observations suggest that the first monolayer structure is similar to that of the molecular plane of the methanol crystal except that all the methyl groups are displaced above the plane containing the oxygens bonded to the metallic substrate. © 1990.