Double beam FT-IR reflection spectroscopy on monolayers

For in situ infrared studies of ultrathin films deposited on solid substrates or spread at an air/liquid interface, we have developed a new FT-IR double beam approach based on differential reflectivity by polarization modulation. Because only the s-component (perpendicular to the plane of incidence) of the electromagnetic field is incident on the studied surface, the spectral Features are easy to interpret in terms of molecular orientation. Spectra of a cadmium arachidate Langmuir-Blodgett film deposited on a gold mirror and a DMPC Langmuir film spread at the air/water interface are reported, to illustrate the advantages of this method.