Photoionization yields, , calculated from Eqs. (4) and (5) for PAH cations with N_C = 34, 48, and 60 atoms. The photoionization yields, Y [N_C](hν), for N_C = 34 and 60, are displayed for comparison. These latter were estimated using Eqs. (4) and (5) from Jochims et al. (1996) adapted for neutral PAHs but taking into account the shift of the ionization potential to IP²⁺, which is relevant for cations. The dashed vertical line marks the 13.6 eV photon energy cut-off for H I regions.