The contribution of Oxygen to the “30”, “26” and “20” μm features

The IR absorption spectra of several macromolecules of interest for amorphous carbonaceous cosmic dust were simulated by means of a commercially available stateof-the-art chemical code. None of the three unidentified far IR features show up significantly in the absence of oxygen in the structure. By contrast, peripheral OH (hydroxy) gives rise to strong modes in the “30” band. The “26” and “20” bands are brought forth by O-bridges and O-substituted 5-membered carbon rings and enhanced by the OH’s. A few similar macromolecules containing various small amounts of oxygen in these three forms and combined in various proportions are enough to qualitatively fit typical dust spectra recently extracted from ISO observations.