H₂CN⁺ · nN₂ clustering formation and the atmosphere of Titan

Abstract

Measurements performed by Voyager 1 have revealed a dense atmosphere around Titan mainly composed of N₂ with some CH₄ and other minor components, including hydrocarbons and organic–nitrogen molecules^1–4. Based on Voyager and some laboratory data, it is reasonable to assume that other complex organic–nitrogen molecules are formed in Titan's atmosphere^5–7. Three-body association reactions are probably involved in the synthesis of such compounds^5,7,8. It has been suggested⁵ that the clustering of H₂CN⁺ with N₂ or CH₄ could have an important role in these reaction mechanisms. Recently,⁸ we observed the H₂CN⁺ · N₂ cluster ion in a N₂–CH₄ mixture irradiated by α particles. Here we report the results of laboratory measurements of equilibrium constants for the clustering of N₂ with H₂CN⁺ leading to H₂CN⁺ ⋅ nN₂ (n = 1–6) formation, which should help in understanding the ion–molecule chemistry in the atmosphere of Titan.