Diffuse Interstellar Bands (DIBs) are a (ever increasing) set of about 300 absorption features superposed on the interstellar extinction curve. They fall in the range from 400 to 1000 nm, and exhibit a full width at half maximum ranging from less than 1 up to 30 angstroms. Since Merrill (1934), DIBs were seen towards more than a hundred sight lines, showing differences in profile shapes and varying relative strengths from one environment to another. This hinted an origin due to a variety of carriers, and many hypotheses have been formulated, ranging from dust grains to several gas-phase free molecules. Nowadays, high resolution observations show partially resolved components inside the profile of some DIBs; this fact, combined with their nearly constant rest wavelength irrespective of the direction of observation, suggests that gas-phase polyatomic molecules are very likely to be responsible for their production.
In particular, complex carbon based molecules, such asPAHs, fullerenes and linear carbon chains, which are thought to be ubiquitous in the ISM, have been proposed as attractive candidates. However, no definitive match between any DIB and any individual such molecules exists to date. The AstroC-Hemistry Group did collect a rather large number of high resolution and high signal-to-noise ratio spectra, most of which were published in a number of papers. The observational activity still continues, in effort to match the laboratory and theoretical suggestions.