The discovery of carbon dioxide (CO₂) in several sources was reported in 1989 by d'Hendecourt et al. using instrumentation on the IRAS spacecraft. As a molecule without a permanent dipole moment, CO₂ was identified via one of its characteristic vibrational features, the bending mode shown, rather than by rotational spectroscopy. Also unusual is that this feature is observed in icy grain mantles rather than in the gas phase.

Carbon dioxide is a well-known terrestrial molecule. It is a by-product of metabolism expelled in animal respiration. It is a principal greenhouse gas in the atmosphere. Frozen, it is known as dry ice.

Carbon dioxide has a second mode that can also be seen in the infrared, the asymmetric stretching mode shown below.