Studies with synthetic single-peak systems have provided information on a range of factors capable of limiting the utility of Fourier deconvolution for peak finding in vibrational spectra. The merits of six apodization functions for controlling Gibbs oscillations resulting from truncation and background effects have been determined. The triangularsinc and triangular-squared functions are the most effective, and the Gaussian function is the least satisfactory. The presence of asymmetry and a degree of Gaussian character in the band shape should not prove a serious limitation for most qualitative and quantitative applications. The peak heights following deconvolution are linear functions of the resolution enhancement factor, K, the constant of proportionality being determined by the particular apodization function employed. By contrast, the areas of deconvoluted bands are sensibly independent of the apodization function. This factor opens the way to quantitative studies on deconvoluted band systems.
Resolution enhancement by the use of Fourier self-deconvolution has been achieved with Raman spectra obtained from an instrument with an intensified diode array detector. A minimum signal-to-noise ratio of about 500:1 is acceptable and this is readily attainable, by spectral accumulation, in the case of relatively strong peaks such as those of carbon tetrachloride at 549 cm−1 and tetrahydrofuran at 915 cm−1. Resolution enhancement factors, K, of about 2.7 are then achieved. Weaker peaks, typified by the v (C-Cl) modes of polyvinyl chloride) require more extensive spectral accumulation, but a K value of 2.2 has proved feasible. The finite resolution imposed by the diode array detector is not a significant limitation. In order to obtain consistently good results it is necessary to optimize the signal-to-noise ratio, by choosing instrumental operating conditions best suited to specific samples.
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