Jacek Krelowski (Center for Astronomy, Nicolaus Copernicus University)
Absorption spectra of translucent interstellar clouds contain continuous extinction (caused by dust grains) and many known molecular bands: of CN, CH+, CH, OH, OH+, NH, C2 and C3.
Moreover, one can observe more than 400 unidentified absorption features known as diffuse interstellar bands (DIBs) commonly believed to be carried by some complex, carbon bearing molecules (chain species based on a carbon skeleton, polycyclic aromatic hydrocarbons, fullerenes). DIBs are unresolved optical features observed in absorption in starlight crossing diffuse interstellar clouds. Despite many laboratory-based studies of possible DIB carriers, it has not been possible to unambiguously link these bands to specific species. So far only three out of more than 400 DIBs (Hobbs et al., 2008) have been linked to specific molecules but none of these links was confirmed beyond a doubt. It seems quite evident that physical properties of dust particles are related to abundances of simple molecular species as well as to those of DIB carriers. The interstellar chemistry seems thus very complex - requiring a lot of observational and experimental work to identify the mysterious DIB carriers.