Resolution and instrument line shape effects on spectral compensation with Fourier transform infrared spectrometers

The effect of limited instrument resolution on spectral subtraction experiments performed using Fourier transform infrared spectrometers is examined from a theoretical standpoint and the predicted results are tested experimentally. For weak absorption bands, boxcar truncation is found to yield better compensation than triangular apodization. For strong bands, whose peak absorbance is greater than one, there are certain conditions under which boxcar truncation leads to better compensation and others where triangular apodization is preferable. The results are discussed in terms of removing strong solvent bands from solution spectra, compensating atmospheric absorption bands, and measuring the effects of intermolecular interactions. The effect of a triangular slit function on subtraction experiments performed using spectra measured with grating monochromators and the possibility of using other apodization functions to improve the results on Fourier spectrometers are also discussed.