Abstract
In this article, some of the more common techniques for processing infrared spectra are summarized, with an emphasis on spectra measured using Fourier transform (FT) infrared spectrometers. They include the conversion of an interferogram to a single-beam spectrum, the ratioing of two single-beam spectrums to yield a transmittance spectrum, and the conversion of a transmission spectrum to an absorbance spectrum. The first- and second-order corrections of attenuated total reflection spectra to give them an appearance more similar to that obtained by transmission spectrometry are discussed next. This is followed by brief discussions of the Kramers–Kronig transformation of specular reflection spectra and the conversion of diffuse reflectance spectra to a form closer to the absorbance spectrum by the Kubelka–Munk conversion. Various apodization functions and their effect on the instrument line shape function are then described. The way in which spectra may be smoothed by the moving average and Savitzky–Golay algorithms is described. The use of FTs for smoothing, conversion to the first- and higher-order derivatives, and resolution enhancement (Fourier self-deconvolution) by the application of appropriate weighting functions is then discussed. Baseline correction and interpolation algorithms are then summarized. Finally, spectral curve-fitting using the Levenberg–Marquardt method to determine the goodness-of-fit is described.
Published Version
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