Formation of complex molecules in Titan's upper atmosphere

Determination of the density of photochemical species in the upper atmosphere is crucial to development of an understanding of chemistry on Titan. Only high-energy photons, electrons, or ions can break the strong N2 bond and these are found primarily in the upper atmosphere. The Ion and Neutral Mass Spectrometer (INMS) performed the first composition measurements of Titan's ionosphere. Approximately 50 ion species were detected on Titan's night side during the T5 close pass by the Cassini spacecraft through Titan's upper atmosphere. We combine modeling and laboratory simulations to analyze and interpret the ion mass spectra measurements made by the INMS. With a model for the chemical kinetics, we identify ions, estimate reaction rates in the atmosphere, and constrain neutral densities. To help identify ions and reveal chemical pathways, we rely on laboratory simulations of complex ionospheric chemistry. The presence of many ions can only be understood as the consequence of significant density of associated neutrals. We have identified 45 ion species and we have determined the abundance of 9 neutral species from analysis of the low mass portion of an INMS ion spectrum, including 4 new N-containing species (NH3 , C2 H3 CN, C2 H5 CN, and CH2 NH). We now extend our analysis to higher altitude regions and to heavier masses. The photochemical products created in the upper atmosphere are highly reactive and it appears that much of the chemistry on Titan occurs in this region rather than at lower altitudes. This affects the composition of the bulk atmosphere, the composition and optical properties of the aerosols and the flux of condensable material to the surface.