Optimization of electrochemical infrared reflection absorption spectroscopy using Fresnel equations

To enhance the signal-to-noise ratio of electrochemical in situ IRRAS techniques, experimental conditions such as the angle of incidence and the thin cavity thickness Should be optimized. Software which utilizes the Fresnel equations ill matrix form was used to determine the experimental conditions at which the maximum in the mean Square electric field strength (MSEFS) at the electrode Surface is obtained. Calculations were done for Au in the mid infrared range from 4000 to 800 cm(-1) for six systems combined of three common IR windows (CaF2, BaF2 and ZnSe) and two electrolyte solvents (H2O and D2O). It was determined that the angle of incidence strongly depends on the refractive index of the electrolyte material, and that approximate values of the optimum angle of incidence can be found using a simple model and Snell's law. It was also shown that the thin cavity thickness affects the performance of the experimental setup via the phase shift of the radiation due to transmission through the solvent. The effect of the window materials and collimation on the experimental conditions is also discussed. The paper is designed to help researchers select the experimental conditions that optimize the performance of their spectroelectrochemical setup. (c) 2007 Elsevier Ltd. All rights reserved.