X-RAY-SCATTERING ANALYSIS OF THE AVERAGE POLY-CYCLIC AROMATIC UNIT INARGONNE 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 bet ween carbon atoms in the mean poly-cyclic aromatic (PCA) unit is appro x. 7.5 Angstrom. The radial-distribution function indicates that, on t he average, each carbon 2.2 nearest carbon neighbors at an average dis tance of 1.43 Angstrom. This information is consistent with the interp retation that 27% of the C-C bonds in this coal involve at least one a lkyl carbon, while 73% of the C-C bonds are between aryl carbons. Comp arisons of the atom-pair correlation function to simulated one-dimensi onal 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 ou r X-ray scattering data. Interpretation of the atom-pair correlation f unction also suggests that the alkyl carbons are predominantly, if not exclusively, bonded to the PCA unit. (C) 1997 Elsevier Science Ltd.