STRAIGHT-CHAIN ALCOHOL ADSORPTION ON THE AG(110) SURFACE

As models for the boundary layer films formed on lubricated metal surfaces we have examined the surface chemistry of a set of straight-chain alcohols on the clean Ag(110) surface. Consistent with previous studies of methanol and ethanol on this surface we find that all these alcohols are adsorbed completely reversibly. The heats of adsorption increase incrementally with addition of methylene groups to the hydrocarbon chain following the form delta-H(ad) = 8.6 + (1.1 +/- 0.1)n kcal/mol for CH3(CH2)n-1OH. The formation of a monolayer of methanol on the surface reduces the surface work function by 1.15 eV, whereas for the longer chain alcohols this number is decremented by approximately 0.085 eV per additional methylene group in the chain. The orientation of the alkyl chain with respect to the surface has been determined with the use of quantitative measurements of X-ray photoemission from the C(1s) and O(1s) levels. We find that the alkyl chains are oriented roughly parallel to the surface rather than forming densely packed films of a Langmuir-Blodgett type.