Fourier transform infrared attenuated total reflection and transmission spectra studied by dispersion analysis.

Fourier transform infrared transmission (FT-IR) and attenuated total reflection (ATR) spectra of water-ethanol mixtures are recorded and reconstructed thanks to a causal dispersion analysis technique. As expected, the Beer's law technique is an empirical approximate method that cannot account for complex spectral features. On the other hand, a rigorous analysis performed by using the theoretical optical paths for both experimental techniques and Gaussian dispersion analysis (GDA) allows the dielectric functions of the pure liquids to be calculated. Simulations of the whole mid-infrared spectra in the range 500-4000 cm(-1) match the experimental data very well, whatever the water-ethanol mixtures. This method is a powerful tool to quantify such model mixtures and more generally could be the first step toward software for assistance to the FT-IR spectrum analysis.