INELASTIC NEUTRON-SCATTERING STUDY OF THE PROTON DYNAMICS IN CARBONS AND COALS

The INS spectra from 30 to 4000 cm(-1) of four coal samples at 20 K with various ranks (subbituminous A, low volatile bituminous, semi-anthracite, and anthracite) are reported. For each sample, rather broad bands superimposed on a continuum with constant intensity over the whole frequency range are observed. This continuum is assigned to recoiling free protons located between the graphite-like planes. The INS spectra of the coals are also compared to that of perylene (C20H12). The spectrum of the anthracite is dominated by the C:H and skeletal modes of polyaromatic entities. Samples of lower rank show bands due to alkylic and vinylic CH2 and CH3 groups. The integrated intensities of the INS spectra are not proportional to the numbers of protons given by the elemental analysis. This is due to different proportions of free and bound protons in the samples. A comparison of the INS intensities in the CH stretching region for coals and perylene gives an estimation of the concentration of bound protons which ranges from similar to 40% to similar to 80%.