Chemistry of Titan's atmosphere

Abstract

Understanding Titan's atmospheric chemistry is a daunting task because of the multiplicity of chemical as well as physical processes involved. Chemical processes begin with the dissociation and/or ionization of the most abundant species, N2 and CH4, by a variety of energy sources. The energetic species produced further react to generate a plethora of gaseous molecules that will eventually become heavy enough to become organic aerosols. Thus, molecular growth is driven by gas phase reactions involving radicals and positive and negative ions, all possibly in some excited electronic state, as well as by heterogenous chemistry on the surface of the aerosols. The efficiency and outcome of these reactions depend strongly on the physical characteristics of the atmosphere, namely pressure and temperature. Moreover, the distribution of the species is affected by molecular diffusion and vertical and horizontal winds, as well as escape from the top of the atmosphere and condensation in the lower stratosphere. An illustration of Titan's atmospheric chemistry is presented in Figure 7.1.