Depth Profiling and Signal Saturation in Photoacoustic FT-IR Spectra Measured with a Step-Scan Interferometer

A commercial step-scan FT-IR spectrometer has been used to obtain photoacoustic spectra of carbon black, coals, polymers, and clays. Variation of the external modulation frequency from 40 to 400 Hz shows that saturation affects many of the spectra. Nevertheless, comparison of spectra of oxidized coal with spectra of fresh coal obtained at the corresponding modulation frequencies yields results implying successful depth profiling. Several suggestions for further experiments are also presented.