Dissociative recombination of nitrile ions with implications for Titanʹs upper atmosphere

Nitrile ions are abundant in Titanʹs upper atmosphere and are expected to be lost mainly via dissociative recombination with free electrons. We review in this paper a series of experimental results on the dissociative recombination reactions of nitrile ions known/expected to be present in Titanʹs upper atmosphere. The experiments were all performed at the heavy ion storage ring CRYRING in Stockholm, Sweden, and the results presented here include information on rate coefficients at electron temperatures relevant for Titanʹs upper atmosphere as well as information on the product branching fractions of the reactions. We discuss implications of the results for Titanʹs atmosphere. As an example the presented results support a statement by Krasnopolsky (2009) that nitriles do not degrade to yield N2 again in Titanʹs atmosphere, indicating that condensation and polymerization with precipitation to the surface are their ultimate fate.