1997A&A...323..534D

We present an ionisation model for Polycyclic Aromatic Hydrocarbon (PAH) molecules from which we determine the various size dependant ionisation states expected in different space environments. Maps of ionisation regimes are derived. They allow the estimate of the ionisation fraction of PAH for any given set of parameters (electron density, flux factor and temperature) assuming a typical PAH size of 50 carbon atoms. Moreover, a particular astronomical case is considered: the variation in ionisation states with depth in a typical dense cloud illuminated by a bright B1.5V star.