Vector saturation transfer e.s.r. studies of coal

Abstract

A newly developed spectroscopic method, vector saturation transfer (VST) electron spin resonance (e.s.r.) was applied to characterize coal samples. Five coal samples from different origins were examined using non-linear response parameters of VST-e.s.r. spectroscopy. Application of low microwave power caused the lineshapes of the e.s.r. signals from coal to vary as a function of the modulation phase. Similar but more drastic changes were observed at the higher microwave powers and at the second harmonic display, which allowed the saturation transfer spectra to be sensitively detected. Using the vector concept, the second harmonic display was separated into the amplitude and phase components. The lineshape of the amplitude spectrum shows a nett envelope of the phase variation, which contains information on the electronic and molecular fluctuations. The phase spectrum, another aspect of VST-signal, gives the degree of saturation transfer. The integrated value of the second harmonic display was used to evaluate the total magnitude of the saturation transfer of free radicals in coal. A correlation was found between the integrated value and the carbon content of coal.