Infrared Observation of Intrinsic Modes on Adsorbent Surfaces by Photothermal Beam Deflection Spectroscopy

Abstract

Abstract Boccuzzi et al. 1 pointed out that the infrared (IR) spectra of fine powders, i. e., materials typical of the texture of adsorbents and catalysts, are the sum of (a) nearly bulk modes; (b) - surface modes due both to first-order (surface truncation) and second order (change of the surface bond force constant) effects; and (c) impurities and/or adsorbed species. Studies of the latter have led to the valuable and voluminous literature of “IR of adsorbed species.” The second order effects are also of interest to surface studies, but little information has been available. In an elegant and detailed study of silica, Boccuzzi et al. observed various impurity modes associated with surface hydroxyl groups, and also intrinsic modes associated with the clean silica surface and related to the different strength and geometry of the surface bonds with respect to the bulk. Their observation demonstrated that new surface and subsurface siloxane groups were spectroscopically distinguishable from those characteri...