Br K-Edge X-ray Absorption Near Edge Structure Analyses of Bromine Residue Carbon Compounds Using Full Multiple-Scattering Theory

Abstract

A recent experimental result shows that Br K-edge X-ray absorption near edge structure (XANES) spectra for bromine residue compounds are sensitive to the heat treatment of host carbon compounds. In the present study we attempt to extract useful information on the geometric and electronic structures of these systems by applying a full multiple-scattering approach to XANES analyses. The residue compounds can be classified into three groups on the basis of XANES spectral features. Present detailed analyses provide us some useful information: Group 1, bromine residue compounds are prepared from host carbon compounds heat-treated at 2000–2800°C, where Br2 molecules exist in the interlayer space of graphite. The interlayer distance expands to about 7.8 Å around the Br2 molecules. For heat treatment at 1900°C, the observed spectra are well explained by the superposition of the spectrum for Group 1 and that for Group 2, with a ratio of 3:4. For Group 2 heat-treated at 1500–1750°C, the host carbon compounds includes Br- ions, but no information on the Br-–C correlation has been obtained. For Group 3 heat-treated at 1000°C, the host carbon compounds mainly includes HBr molecules parallel to small aromatic carbon molecules.