The vertical distribution of HCN, $HC_3N$ and $C_2N_2$ have been determined from a sequence of Voyager 1 IRIS limb tangent measurements over Titan's north polar region. This sequence yields gas distributions with ${\sim}200\;km$ altitude resolution over the 50-400 km range. The derived mixing ratios of HCN, $HC_3N$ and $C_2N_2$ are $5{\times}10^{-7}$, $7{\times}10^{-8}$ and $8{\times}10^{-9}$, respectively, at 120 km with a factor of 3 uncertainty.

• Kim Sang-Joon(Institute of Natural Sciences Kyung Hee Observatory, Department of Astronomy and Space Science Kyung Hee University)