PAH charge state distribution and DIB carriers: Implications from the line of sight toward HD 147889

The calculation of charge state fractions of different polycyclic hydrocarbons (PAH) in HD 147889 using diffuse interstellar bands (DIB) was discussed. Different wavelength regions in the DIB spectrum were populated by different PAH charge states depending on the underlying PAH size distributions. The PAH size distribution for HD 147889 was constrained by the observed DIB spectrum to be Gaussian with a mean of 50 carbon atoms. It was observed that the charge state of specific PAHs at a certain extinction in the cloud depended on their ionization potential which in turn depended on the molecular size and the molecular structure.