THE IONIZATION STATE OF PAHS IN INTERSTELLAR ENVIRONMENTS

We present an ionisation model for Polycyclic Aromatic Hydrocarbon (PA H) molecules from which we determine the various size dependant ionisa tion states expected in different space environments. Maps of ionisati on regimes are derived. They allow the estimate of the ionisation frac tion of PAH for any given set of parameters (electron density, flux fa ctor 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 b y a bright B1.5V star.