Hydrocarbon ions in the ionosphere of Titan

We have constructed a new model of the ionosphere of Titan that includes 67 species and 626 reactions. Although N-2(+) is the major ion produced over most of the ionosphere, the ionization flows to ions whose parent neutrals have lower ionization potentials and to ions formed from species with large proton affinities. In contrast to other models, which have predicted that HCNH+ should be the major ion, our calculations suggest that the major ions at and below the ion peak are hydrocarbon ions, and H, C, and N-containing ions. Our predicted peak electron density for a solar zenith angle of 60 degrees is about 7.5 x 10(3) cm(-3) at an altitude of 1040 km.