Quality Evaluation of Polarization-Modulation Infrared Reflection-Absorption Spectra of a Langmuir Monolayer on Water Dependent on Angle of Incidence and Molecular Orientation

Quality analysis of polarization modulation infrared reflection absorption spectrometry (PM-IRRAS) for measurements of a Langmuir (L) monolayer film on water is presented The spectral quality represented by the signal to-noise ratio is evaluated by taking into account both the band intensity and the electrical signal throughput led out from the Fourier transform Infrared (FT-IR) spectrometer The product of the two parameters, which is named the quality evaluation function, theoretically reveals the optimal angle of incidence for the L film measurements In addition, the PM IRRAS-specific surface selection rule with respect to the spectral quality is also presented