Attenuated total reflection (ATR) spectroscopy in the infrared has been applied to the study of the surface structure of various rank coals. No special time-consuming pretreatment of the sample is required which could effect the results. The sample is simply contacted with a reflection element. The method offers a possibility of a spectral study of the surface of the coal samples with graining up to several dozens of micrometers, and the scattering effect is not observed. In the low-temperature (130°C) coal oxidation process a formation of carbonyl and carboxyl groups (the band at 1700 cm<sup>−1</sup>) and a change in intensity for the rest of the bands have been observed. Oxidation of low-rank coals causes changes mainly in the aliphatic groups of the coal, while in the case of the highest-rank coal the changes in the aromatic structures are more marked.
Jerzy A. Mielczarski, Andrzej Deńca, and Jerzy W. Strojek, "Application of Attenuated Total Reflection Infrared Spectroscopy to the Characterization of Coal," Appl. Spectrosc. 40, 998-1004 (1986)