Abstract
In this review, it is described that new information can be obtained by applying new ESR methods to the radicals contained in coals. High frequency ESR measurements enable us to observe the highly resolved ESR signals. Thus, the mechanism of linewidth broadening of the ESR signals for coal radicals can be discussed in terms of the spin exchange, the hyperfine interaction and the anisotropy of g-value. By pulsed ESR measurements, various kinds of spectra such as nutation spectra and HYSCORE (hyperfine sublevel correlation spectroscopy) spectra are obtained. The nutation method confirms the spin multiplicity of coal radicals. The 1H-and 13C-hyperfine signals are separately observed in HYSCORE spectra. In comparison with the model compounds, main coal radicals are attributed to the radicals with highly symmetrically condensed aromatic hydrocarbons.
