X-ray scattering analysis of the average poly-cyclic aromatic unit in argonne premium coal 401

An X-ray scattering study of APC 401 (a coal taken from the Pittsburgh seam), using MoKalpha X-rays, indicates that the longest distance between carbon atoms in the mean poly-cyclic aromatic (PCA) unit is approx. 7.5 Angstrom. The radial-distribution function indicates that, on the average, each carbon 2.2 nearest carbon neighbors at an average distance of 1.43 Angstrom. This information is consistent with the interpretation that 27% of the C-C bonds in this coal involve at least one alkyl carbon, while 73% of the C-C bonds are between aryl carbons. Comparisons of the atom-pair correlation function to simulated one-dimensional structure functions calculated from three-dimensional structural models of several poly-cyclic molecules indicate that a ribbon-shaped C-14 unit (analogous to anthracene) best agrees with the results of our X-ray scattering data. Interpretation of the atom-pair correlation function also suggests that the alkyl carbons are predominantly, if not exclusively, bonded to the PCA unit. (C) 1997 Elsevier Science Ltd.