Thermally excited multiplet states in flame coal

Paramagnetic centres of Polish flame coal with a carbon content of 70.8 wt% were studied by electron paramagnetic spectroscopy at X-band (9.3 GHz). The influence of the measuring temperature on its two-component EPR spectrum was analysed. The measurements of line intensity and linewidth were carried out in the temperature range 100–300 K. It was found that the broad Lorentz line present in the EPR spectrum of the studied coal is responsible for temperature dependence of integral intensity which does not fulfil the Curie law. This proves the existence of thermally excited multiplet states in flame coal. Paramagnetic centres related to the narrow Lorentz line in flame coal obey the Curie law.