A coal model for the carriers of the unidentified IR bands

The absorbance spectrum of vitrinite is shown to come closer to the generic spectrum of the unidentified IR bands (UIB's) than any previously proposed model. Vitrinite is the organic and major component of coal, its composition, structure and behaviour as a function of age, origin, heat, treatment, etc. are now fairly well known. A very large amount of IR data on vitrinite (as well as on the other components of coal) is also available and still accumulating. It appears from all these data that all coals have a limited number of mid-IR features; the factors mentioned above only alter the relative intensities of these features, leaving their positions and widths practically unchanged and identical to those of the UIB's. Each of the UIB's has its counterpart in the vitrinite spectra, which also exhibit a continuum rising toward the blue. The better fit provided by vitrinite over other models is due to the presence of oxygen, as well as hydrogen, in the form of surface functional groups bonded to a bulk, disordered, carbon structure with aliphatic as well as aromatic bonds