Organic molecules with acidic hydrogens, adsorption

In contrast to the minimal activity in infrared reflection studies the technique of inelastic electron tunneling spectroscopy (IETS) recently has contributed a large amount of information on monolayer adsorption of organic molecules on smooth metal oxide surfaces,Q),aluminum oxide layers on evaporated aluminum. These results indicate that a variety of organic molecules with acidic hydrogens, such as carboxylic acids and phenols chemisorb on aluminum Oxide overlayers by proton dissociation - 1 — and that monolayer coverage can be attained quite repro-ducibly by solution doping techniques. - The IETS technique is sensitive to both infrared and Raman modes. — However, almost no examples exist in which Raman il and or infrared spectra have been taken for an adsorbate/substrate system for which IETS spectra have been observed. 

The same picture holds for physical adsorption on metal surfaces. The polarization of the adsorbed molecules causes dipoles pointing with their positive ends away from the metal surface. The work function of the metal will be lowered by this effect, and it seems as if the increase of the normal nonselective photoelectric emission of metals by the adsorption of water molecules (122) or molecules of organic substances such as pyridine, propionic acid, and benzene (123) or alcohol, diethyl ether, and acetone (124) is caused by this effect. The explanation, which, many years ago, was given by the author (125), viz., polarization by positive hydrogen ions which should still be present, may seem to be unnecessary and obsolete. 

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