ELECTRON MAGNETIC-RESONANCE OF STANDARD COAL SAMPLES AT MULTIPLE MICROWAVE-FREQUENCIES

The naturally occurring unpaired electrons in coal provide a unique route for the nondestructive study of coal structure Electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), dynamic nuclear polarization (DNP), and electron spin-echo (ESE) techniques use the paramagnetic spins as probes of their environment, and the spins provide information about their immediate chemical surroundings as well as about the nature of more distant regions in the coal. In the context of an ongoing program in our laboratory to better determine the structure and bonding in the organic (maceral) components of whole coals (including Argonne Premium coal samples), coal extracts, and model coal systems by electron magnetic resonance (EPR, ENDOR, ESE), we have begun a multifrequency EMR study of coal, with the frequency range spanning nearly 2 orders of magnitude (2-250 GHz), to improve our understanding of the complex magnetic interactions present in the coal material and the origin of these effects in molecular structure and bonding. With this approach, we are developing methods for the elucidation of atomic and molecular structure in coal and other complex, disordered materials.