C₂N₂ Vertical Profile in Titan's Stratosphere

In this paper, we present the first measurements of the vertical distribution of cyanogen ($C_2{N}_2$) in Titan's lower atmosphere at different latitudes and seasons, using Cassini's Composite Infrared Spectrometer far-infrared data. We also study the vertical distribution of three other minor species detected in our data: methylacetylene ($C_3{H}_4$), diacetylene ($C_4{H}_2$), and $H_{2}O$, in order to compare them to $C_2{N}_2$, but also to get an overview of their seasonal and meridional variations in Titan's lower stratosphere from 85 km to 225 km. We measured an average volume mixing ratio of $C_2{N}_2$ of $6.2\pm 0.8\times {10}^{-11}$ at 125 km at the equator, but poles exhibit a strong enrichment in $C_2{N}_2$ (up to a factor 100 compared to the equator), greater than what was measured for $C_3{H}_4$ or $C_4{H}_2$. Measuring $C_2{N}_2$ profiles provides constraints on the processes controlling its distribution, such as bombardment by Galactic Cosmic Rays which seem to have a smaller influence on $C_2{N}_2$ than predicted by photochemical models.