Published online by Cambridge University Press: 05 January 2014
7.1 Introduction
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.
Our interest in Titan's chemistry started in the 1970s, when it became apparent that the atmospheric CH4-to-H2 ratio was much larger than that in the atmospheres of the giant planets, rendering Titan's atmosphere better suited for the synthesis of organic compounds. However, ground-based observations indicated that CH4 was the principal atmospheric constituent and, because of this, the photochemical models of Allen et al. (1980) and Strobel (1974) were restricted to hydrocarbon chemistry.
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.