New estimates of ionization potentials of four DIB molecular carriers

We present a study of the behaviour and ionization properties of four Diffuse Interstellar Bands (DIBs) at λλ5780, 5797, 6379 and 6613 Å. In the λλ5797, 6379 and 6613 Å DIBs, substructures have recently been detected, indicating large gaseous molecular carriers. Studying DIBs in regions with different physical properties in terms of UV flux and density enables us to monitor the behaviour of the carriers and hence to constrain their nature. As a follow-up of Sonnentrucker et al. (1997), we add new lines of sight and generalize the results for lines of sight with 2 or 3 clouds. This refines the Ionization Potential estimates which are between 10 and 13 eV, hence reminiscent of PAH or fullerene cations for those DIBs.