SNIFTIRS STUDIES OF THE DOUBLE-LAYER AT THE METAL-VERTICAL-BAR-SOLUTION INTERFACE .1. SINGLE-CRYSTAL GOLD ELECTRODES IN AQUEOUS PERCHLORIC-ACID

In situ infrared reflection spectroscopy has been used to probe the co ncentration change of the perchlorate anion in the electrical double l ayer at low-index single crystal gold electrodes. Cyclic voltammetry w as used to estimate the amount of anionic charge in the diffuse layer, assuming the absence of specific adsorption near the potential of zer o charge (pzc). A correlation between the integrated intensity of the perchlorate band at 1109 cm(-1) and the surface excess of the anion in the diffuse layer estimated by the Gouy-Chapman theory was found for sigma(m)<\10 mu Ccm(-2)\. At higher positive charge densities on the m etal, systematic deviations were observed. A strategy to determine the pzc at the higher concentration of perchloric acid (1 M), which is no t available from electrochemical techniques, is presented. This involv es the previous determination of the effective extinction coefficient of the perchlorate anion in the double layer. This parameter was deter mined from the analysis of integrated IR bands at a lower concentratio n (0.1 M), for which the cyclic voltammogram provides the value of the pzc, Based on these results it is shown that SNIFTIRS data can be use d to confirm the location of the pzc in both dilute and concentrated s olutions under circumstances where more traditional techniques cannot be used.