Ethylene in the circumstellar envelope of IRC+10216

Ethylene (C₂H₄) is a symmetric molecule that is best detected using mid-infrared transitions. We report on observations of the 10.5 μm ν₇ band using the cryogenic grating spectrograph TEXES. These confirm the previous ethylene detection in the IRC+10216 circumstellar shell. We detect 18 ethylene lines. The lines are both narrow and weak with depths of no more than ~2%. The ethylene lines suggest an excitation temperature of ~80 K.