Revised infrared bending mode intensities for diacetylene (C4H2): Application to Titan

• Infrared spectra in far and mid-infrared of diacetylene with a pure sample.
• Large revision of previously measured band intensities.
• Consequences on abundance determination in astrophysical environments and in particular Titan׳s atmosphere.

Diacetylene (C4H2) has been observed in various astrophysical environments in the infrared range through the bending modes ν8 at 628.0 and ν9 at 220.1 cm−1. Accurate intensity measurements of both modes are necessary to obtain precise abundance determination. Laboratory spectra covering both bending modes have been recorded with a pure diacetylene sample. Precise band intensities have been measured showing large discrepancies compared to previous studies, reaching a factor 2.3 for the ν9 band and a smaller difference of 20% for the ν8 band. Consequences on the determination of abundances of diacetylene in Titan׳s atmosphere are discussed.