This paper concerns the possible orientation of water molecules at the surface of platinum electrodes in aqueous NaF solutions. The work was carried out by using in situ FTIR spectroscopy in SNIFTIRS (substractively normalized interfacial Fourier transform infrared spectroscopy) mode. The intensity of the IR spectral band around 3300 cm"1 11, characteristic of O-H vibration, was found to increase from about 0.0 V on the NHS when the potential was shifted anodically. Corresponding bands were observed for the O-D stretch in a 50-50 H20-D20 mixture. However, the intensity of these were 4-8 times less than those for the O-H vibration. This difference is explained in terms of their differences in hydrogen bonding. The dependence of the intensity of OH and OD vibration upon potential fits a model for water orientation in which water molecules lie flat (i.e., both oxygen and hydrogen atom of a water molecule lie on the surface) near the pzc and gradually orient with their oxygen end toward the surface with the increase of electrode potential in the anodic direction. The results would also probably fit other models in which the water dipoles change their direction on change of electrode charge.

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The paper represents an FTIR study of the adsorption from aqueous solutions of phosphoric acid onto Pt and Au electrodes at various concentrations and potentials. The experimental method utilizes parallel polarized light; the light path through the solution is around 10−4 cm. The signal‐to‐noise ratio was made acceptable by subtracting spectra obtained in regions in which H3PO4 was known from radiotracer measurements not to be adsorbed from the spectra at potentials at which adsorption occurs. It was found that there is one main peak at 1074 cm−1 which varies parabolically with potential. Values of the electrode coverage, θ, were obtained by calibrating the peak heights against the results of parallel radiotracer measurements. Plots of θ against logC are linear. The adsorption maximum on Au was ca. 300 mV more positive than that on Pt. The validity of the measurements is supported by the rational trends of the data obtained, in particular, the relation to the spectroscopic data separately obtained for H3PO4 in solution. H3PO4 in solution is 99% molecular and 1% ionic. It is shown that the coverage data can be evaluated in such a way (solvation of H3PO4 ) that 0.2<θ<0.6 , so that a Temkin isotherm may be applicable. The difference in results on Au and Pt may not be interpreted unambiguously in terms of displacement by oxide: accounting for water bonding appears necessary. The method offers an alternative to SERS.