Using SOFIA’s EXES to Search for C ₆ H ₂ and C ₄ N ₂ in Titan’s Atmosphere

Abstract In Titan’s atmosphere, the chemistry of simple hydrocarbons (e.g., CH 4 and C 2 H 2 ) and nitrogen bearing species (e.g., N 2 and CN) represents an important link between molecular species and the ubiquitous organic haze that gives Titan its characteristic orange hue. Here we present a new search for two previously undetected molecules, triacetylene (C 6 H 2 ) and the gas phase dicyanoacetylene (C 4 N 2 ), using the Echelon-Cross-Echelle Spectrograph instrument on board the Stratospheric Observatory for Infrared Astronomy aircraft. We do not detect these two molecules but determine upper limits for their mixing ratios and column abundances. We find the 3 σ upper limits on the uniform volume mixing ratio (VMR) above 100 km for C 6 H 2 to be 4.3 × 10 −11 , which is lower than the photochemical model predictions. This new upper limit suggests that the growth of linear molecules is inhibited. We also put a strict upper limit on the uniform VMR for gas phase C 4 N 2 above 125 km to be 1.0 × 10 −10 . This upper limit is well below the saturation mixing ratio at this altitude for C 4 N 2 and greatly limits the feasibility of C 4 N 2 forming ice from condensation.