2-DIMENSIONAL EPR SPECTROSCOPIC STUDIES ON THE RADICALS IN ARGONNE PREMIUM COALS

Two-dimensional electron paramagnetic resonance (BD-EPR) spectra of Il linois No. 6 and Upper Freeport coals have been measured. From 2D-nuta tion spectroscopy, it is confirmed that the main EPR signal around g = 2 is attributed to free radicals, but not to radical pairs. Both coal s showed nuclear modulation effects due to H-1 and naturally abundant C-13 nuclear spins. Spin-echo correlation spectroscopy (SECSY) experim ents elucidate the distribution of modulation frequencies included in a broad EPR spectrum. The observed dip in the C-13 matrix spectrum obt ained from SECSY is interpreted in terms of the decrease of vitrinite radicals, which are weakly interacting with C-13 nuclei, in the centra l region of the EPR spectrum. The analysis of the broad hyperfine spec tra due to H-1 and C-13 nuclei in the hyperfine sublevel correlation s pect-ra suggests the existence of several kinds of radicals in coal. M ost of unpaired electrons are considered to be trapped in aromatic rin gs. The ratio of C-13/H-1 of hyperfine spectra increases with coal ran k, suggesting a new index of coal rank.