Infrared spectroelectrochemical configurations for in situ measurements

The choice of infrared (IR) spectroelectrochemical configurations and accessories depends on the type of reaction investigated. The mostly used system is Otto configuration where the electrolyte is squeezed between the electrode and the internal reflection element (IRE). However, another system with the film electrode deposited directly onto the flat side of the IRE (Kretschmann configuration) gains popularity, not only because of the increase in sensitivity, but also as it allows electrochemical reactions involving gas evolution. By the use of Fresnel equations for three-phase stratified medium we show that the strength of mean-square electric field (MSEF) at the metal/solution interface, associated with the dissipation of energy onto the adsorbed species in Otto configuration, is rather flexible in the choice of the optimal angle of incidence of the IR radiation and the thickness of the water layer. On the other hand, Kretschmann configuration is very sensitive to the parameters of the optical system, so the calculations of the MSEF are necessary to identify the optimal angle of incidence and the thickness of the metal layer that give maximal enhancement in the mid-IR region where the bands of interest occur.