Knowledge Bank

The infrared spectra returned by Voyager 1 of the atmosphere of Titan Saturn's largest moon, have shown the presence of eleven gaseous molecular $species.123$ All of these previously reported species are compounds of hydrogen, carbon, and nitrogen. We have now identified a feature in the Titan spectra at $657cm-1$ as being due to the $\nu 2$ Q-branch of carbon dioxide. The identification of $CO2$ is based on frequency correspondence between observed spectra and laboratory measurements, and on the elimination of alternative species which might be present in Titan's atmosphere. A mole fraction of $7\times 10-10$ has been determined for $CO2$ from the $667cm-1$ feature.