The problem of obtaining the infrared spectrum of a molecular monolayer adsorbed on a bulk metal is discussed. The intensity of an infrared absorption band in radiation reflected from the surface is calculated for (a) various optical constants of the adsorbed layer and the metal, (b) various thicknesses of the adsorbed layer, (c) various angles of incidence, and (d) both states of polarization of the incident radiation. The absorption factor for infrared radiation polarized parallel to the plane of incidence typically has a peak at an incident angle of about 88°, where the absorption is 5000 times greater than at normal incidence. The absorption of a thin layer by the reflection technique, at optimum conditions, is calculated to be about 25 times greater than by transmission through the unsupported film at normal incidence.

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Previous calculations have shown that a thin, moderately absorbing layer on a metal surface has an absorption factor in the infrared which varies greatly with the angle of incidence and the state of polarization of the incident radiation. The requirements on a spectroscopic system, which uses the insights of these calculations, are discussed under the realistic conditions of multiple reflections with a low f/number beam. A method is described for obtaining many reflections between closely spaced mirrors. Radiation emerges from a narrow aperture between the mirrors, the aperture serving as an effective source for the infrared monochromator. A system has been constructed and its use is illustrated by the spectrum of a cellulose acetate layer on a silver mirror.

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The adsorbed surface species which result when aluminum oxide is exposed to methanol or ethanol vapor have been studied. Three different surface species have been identified for both methanol and ethanol. At 35°C a weakly bound layer of liquid alcohol is observed, which is removed by evacuation. Another species which persists after prolonged evacuation is identified as a surface methoxide in the case of methanol and an ethoxide in the case of ethanol. When the alumina sample is heated to 170°C in alcohol vapor a formate-like surface compound is formed from methanol and an acetate-like compound from ethanol. This interpretation of the surface structure has been checked by using deuterated methanols and C13-enriched methanol.

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