Model of Titan's ionosphere with detailed hydrocarbon ion chemistry

We have modified the previous model of Keller, Cravens and Gan (1992, J. Geophys. Res. 97, - 12117) of the ionosphere of Titan. The model is a one-dimensional photochemical model and takes into account newly measured gas phase kinetic rates, particularly those of the higher mass hydrocarbons and nitriles. The model neutral atmospheres developed by, Yung er nl. (1984, Astrophys. J. Suppl. 55, 465), Yung,(1987, Icarus 72, 468) and Toublanc et al. (1995, Icarus 113, 2) were used in our model. The current model includes more neutral and ion species and discriminates among the various higher mass hydrocarbon and nitrile ion species. Ion neutral chemistry produces HCNH+ as the single major ion species at the ionospheric peak (an altitude of 1055 km), however, the total density of all the higher mass hydrocarbons is more than that of HCNH+. The higher mass hydrocarbons include such species as : c-C3H3+, C5H5+, and C3H5+. Another important ion species is H2C3N+. Based on this model Mle expect the higher mass channels (e.g. 39 amu, 41 amu, 53 amu, 65 amu, 67 amu, and 69 amu) of the Cassini Ion-Neutral Mass Spectrometer to measure higher densities than previous models have predicted. (C) 1998 Elsevier Science Ltd. All rights reserved.