Simulation and experimental approaches were utilized to demonstrate that the direction of spectral features of the electrochemical in situ PM IRRAS depends upon the position of the electrode within the spectroelectrochemical cell This behavior is the result of an increasingly stronger interaction of s-polarized radiation with an aqueous electrolyte at larger window-electrode separations Thus the best performance of the experimental setup is expected for separations between the electrode and window that are smaller than the crossover point where the reflectivities for p- and s-polarized light are equal Positive bands or upright peaks should be observed for these experimental conditions Additionally the correlation between simulated and experimental spectra is improved by maintaining the aperture of the optical bench between 10% and 15% (C) 2010 Elsevier B V All rights reserved