Polyynyl-substituted PAH molecules and DIB carriers
  Polycyclic aromatic hydrocarbon (PAH) molecules have been long considered
promising candidates for the carriers of the diffuse interstellar bands (DIBs).
The PAH-DIB hypothesis, however, raises two major issues. First, the number of
interstellar PAH species is potentially orders of magnitude larger than the
number of DIBs. Second, the absorption spectrum of a PAH is in general
dominated by bands found at UV wavelengths while, conversely, DIBs are absent
from the UV wavelength domain and arise at visible and near IR wavelengths.
These issues do not necessarily weaken the PAH-DIB hypothesis and can actually
allow us to refine it. In that context, we analyze the UV/vis absorption
spectra of PAH molecules isolated in Ne matrices and propose that
polyynyl-substituted PAHs, or similar species, are valid candidates for the
carriers of the DIBs. Finally, a possible lifecycle for DIB-carrying PAHs is
presented.
