The potential-dependent specific adsorption of acetic acid and acetate at polycrystalline platinum-and goldaqueous interfaces has been examined by potentialdifference infrared spectroscopy (PDIRS) in conjunction with quantitative surface concentration measurements using the radiotracer technique. Both the infrared and radiotracer measurements utilize a similar thin-layer solution arrangement. Extensive adsorption of acetic acid occurs at both platinum and gold, which increases at more positive potentials and reaches a maximum at the onset of anodic oxide formation. The PDIR spectra contain several features identified with solution acetic acid in the 1200-1800-~m-~ region, including vC4 and vC4 bands at 1710 and 1280 cm-I, respectively, arising from adsorption-induced changes in the thin-layer solution composition as well as a single band, at 1415 and 1400 cm-' on platinum and gold, respectively, due to adsorbed acetic acid. The intensity of the former bands can be employed to evaluate the extent of adsorption as a function of potential; the results are in semiquantitative agreement with the surface concentration-potential data from radiotracer measurements. Although the radiotracer measurements indicate that acetate is not significantly adsorbed, acetate solutions in unbuffered media also yield intense PDIR spectra at platinum and gold, the latter arising merely from pH-induced changes in the thin-layer solution composition associated with anodic oxide formation. The 1400-cm-' feature for adsorbed acetic acid is consistent with a symmetric carboxylate stretching mode; the absence of the corresponding asymmetric vibration is indicative of a C, geometry with both carboxylate oxygens oriented toward the metal surface. In view of the infrared spectra together with the observed absence of acetate adsorption, the most likely modes of acetic acid adsorption involve hydrogen bonding between the carbonyl oxygen and inner-layer water molecules, or by self-association to form dimers or chain structures. a grant (to A.W.) from Dow Chemical Corp. , 71-50-1; Pt, 7440-CHE-85-13732 to M.J.W.).The equivalent parallel conductance technique was used to study surfacestate behavior at the n-CdSe single crystal/aqueous sulfide interface. Surface states were found at -1.1 V versus SCE (-0.6 eV below the conduction band minimum) in solutions containing hydroxide and sulfide. The phase-sensitive photocurrent was affected by these states. Addition of dissolved sulfur to the solution removed the hump in the conductance versus voltage curves caused by these states and the photocurrent behavior is also improved.

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A radioelectrochemistry instrument has been constructed in order to characterize adsorbates on smooth electrodes, in situ. The instrument is described, and preliminary results are discussed. A smooth, polycrystalline electrode is pressed against a glass scintillator detector in order to reduce the solution background count rate to manageable levels. After the linearity of the system was confirmed by using NaHI4CO3 in solution, the kinetics of HI4COOH adsorption and the potential dependence of [2,6-14C]pyridine adsorption were measured. At a bulk surfactant concentration of M, the sensitivity of this technique is about 1% of a monolayer. Adsorption kinetics of processes occurring on a time scale of seconds can be measured. This technique is expected to complement both in situ and ex situ surface electrochemistry spectroscopies.The formation of zeolite Y from colloidal silica and soluble silicate species was investigated by Raman spectroscopy. The role of aging of the reactant mixture was studied. During the nucleation period, the solid amorphous phase consists of predominantly six-membered aluminosilicate rings, which act as building blocks for the formation of zeolite Y . It is essential to have polymeric, highly condensed silicate units as a reactant if zeolite Y crystallization is to take place.

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