Abstract
The complex lineshape of the X-band EPR spectra of natural coal heated at 300–650 °C was numerically analysed. The experimental spectra were approximated by superpositions of one Gauss and three Lorentz lines. Linewidths (ΔHpp), g-factors and abundances of the components of the total spectrum were evaluated. The total concentration and concentrations of the four types of paramagnetic centres in the coal samples were determined. Two groups of unpaired electrons with strong dipolar interactions responsible for broad Gauss (ΔHpp = 0.68–0.92 mT) and broad Lorentz (ΔHpp = 0.54–0.64 mT) EPR components and two groups of unpaired electrons with exchange narrowed Lorentz lines (ΔHpp = 0.17–0.24 and 0.06–0.08 mT) were detected. Dipolar interactions of unpaired electrons with broad lines changed considerably during the thermal decomposition of coal. A strong influence of atmospheric oxygen molecules on magnetic interactions of unpaired electrons with the broad Gauss and the two narrow Lorentz lines was observed. Copyright © 1999 John Wiley & Sons, Ltd.
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