DECONVOLUTION AND CURVE-FITTING IN THE ANALYSIS OF COMPLEX SPECTRA - THE CH STRETCHING REGION IN INFRARED-SPECTRA OF COAL

Numerical techniques are widely used to analyze spectra comprising overlapping bands. In principle, curve-fitting yields the most information, provided that the assumptions concerning the number of bands and their shapes are valid. Deconvolution is an effective means of estimating the number of bands and their positions, but this method is sensitive to noise and can produce spurious features which may be misinterpreted as being genuine. In this paper, we have combined curve-fitting with a nonlinear deconvolution technique to examine the CH stretching region of the infrared spectra of two different coal samples. The probable number of bands and their approximate frequencies were obtained by deconvolution of the measured spectra and then used in the fitting calculation. In order to choose between band shapes yielding fits of comparable quality, the fitted spectra were deconvolved and the results compared with the deconvolution of the original spectra. The samples analyzed were a Western Canadian vitrinite (separated coal maceral) and a lignite (low-rank coal). We conclude that the CH region of the photoacoustic spectrum of the vitrinite contents of twelve Voigt bands, while the diffuse reflectance spectrum of lignite is made up of ten Gaussian bands.