Condensed species in Titan's stratosphere: Confirmation of crystalline cyanoacetylene (HC3N) and evidence for crystalline acetylene (C2H2) on Titan

Infrared spectra of crystalline HC3N and C2H2 were investigated at several temperatures between 15 and 150 K. The characteristics of the 505 and 753 cm−1 bands of HC3N are in complete agreement with the emission spectral data on Titan obtained by the Voyager IRIS instrument, thus confirming the identification of crystalline HC3N on Titan. A composite spectrum in the 720-800 cm−1 region, with contributions from HC3N and C2H2 in crystalline phases, reproduces the Voyager emission data in that region, thus providing a suggestion for the identification of crystalline C2H2 on Titan.