Prediction of a N2++ layer in the upper atmosphere of Titan

Abstract : Calculations of dication N2 ++ density in the atmosphere of Titan is performed for the first time. The metastable lifetime of this species is 3 seconds in its ground state. The density of the N2 ++ layer centred around 1100–1200 km altitude can reach 104 m−3. The ions are produced by both the double photoionisation and the photoelectron impact of N2. They are lost by dissociative recombination with the thermal electrons and chemical reactions with N2 and CH4. The most recent chemical reaction rate constants, given by laboratory experiments, were used in this study. Finally, we explore the possible detection of this ion layer by a spectrophotometer and show that the UVIS instrument onboard CASSINI could be capable to observe it.