Laboratory studies of polycyclic aromatic hydrocarbons, fullerenes and linear carbon chains in an astrophysical context

The spectroscopic and photophysical properties of a number of molecular species that have been proposed as carriers of particular features of the interstellar extinction curve are discussed. Neutral and ionic polycyclic aromatic hydrocarbons (PAHs). fullerenes and the carbon chain species Cn, polyenes, polyynes and polyynyl radicals, are reviewed in this context. No definitive assignments are given for the 220 nm interstellar peak or the diffuse interstellar band (DIB) carriers, but the spectral analysis concerning current data on the contending proposed carriers favours a recent suggestion that some of the DIBs are due to polyynyl radicals CnH. From the observed profiles and widths of the DIBs, it is concluded that their molecular carriers must contain more than 10–15 atoms.