HYDROCARBON IONS IN THE IONOSPHERE OF TITAN

We have constructed a new model of the ionosphere of Titan that includ es 67 species and 626 reactions. Although N-2(+) is the major ion prod uced over most of the ionosphere, the ionization flows to ions whose p arent neutrals have lower ionization potentials and to ions formed fro m species with large proton affinities. In contrast to other models, w hich have predicted that HCNH+ should be the major ion, our calculatio ns suggest that the major ions at and below the ion peak are hydrocarb on 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.