Design and performance of a flow-through polarization-modulation infrared reflection-absorption spectroscopy cell for time-resolved simultaneous surface and liquid phase detection under concentration and temperature perturbations.

Design and performance of a flow-through cell for polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) suitable for simultaneous monitoring of species on surface and in liquid phase on a molecular level at a high time resolution (ca. 1 s) are presented. In particular, the cell was designed to allow periodic concentration and temperature perturbations and thus excite physicochemical phenomena of interest occurring at solid-liquid interfaces. Utilizing the perturbations and spectral responses of both surface and liquid phase species, their dynamic behavior, kinetics, and correlations can be studied. The detection sensitivity is greatly enhanced by the data processing employed in modulation excitation spectroscopy (MES). The cell design is based on a theoretical model. The IR beam path through a multiple-phase system consisting of air, prism, and liquid as well as light reflection at the surface of a sample were considered in order to maximize the detected IR light intensity and absorption by surface molecules. Its high surface sensitivity was demonstrated by CO adsorption on a thin Pt film in a liquid phase. Combination of the PM-IRRAS with concentration MES led to a significant sensitivity enhancement for the detection of surface and liquid phase species. The temperature, tunable in a wide range from 263-343 K, could be controlled within an accuracy of 0.1 K and also modulated periodically in a completely reversible manner, thus allowing accurate temperature MES experiments. With these capabilities, dynamic physicochemical processes at solid-liquid interfaces can be sensitively investigated.