Reflection Absorption Infrared Spectroscopy

Abstract

Recent case studies are presented that illustrate the capabilities of the technique of reflection absorption infrared spectroscopy (RAIRS) for probing the structure and surface chemistry of model metal catalysts. A key feature of RAIRS is the polarization dependence of the interaction of infrared radiation with surface vibrations. Only the component of polarization parallel to the plane of incidence (p-polarization) interacts with molecules on the metal surface, whereas surface vibrations are invisible to light polarized perpendicular to the plane of incidence (s-polarization). Since both polarizations interact with gas-phase molecules, the polarization dependence of the spectra allows surface vibrations to be distinguished from those of gas-phase species. This is the basis for using RAIRS to study surfaces under ambient pressure conditions, in addition to studies in ultrahigh vacuum. The case studies presented include the use of RAIRS of CO to probe the structure of surfaces, the hydrogenation of acetylene, the activation of CO2 by H2O on a ZrO2 thin-film grown on a Pt3Zr(0001) surface, and the formation of hydrogen-bonded clusters of methanol on a Pd(111) surface.