Cyanogen molecule, showing bond lengths.
Cyanogen (C2N2) is a colorless, toxic gas, a pseudohalogen, prepared by oxidizing a cyanide. It is reactive and polymerizes (see polymerization) to paracyanogen. Melting point -27.9°C, boiling pint -21.2°C.
Cyanogen bands (CN bands) are molecular absorption bands found in the spectra of stars of type G0 and later. Cyanogen absorption is an important luminosity criterion, and is more pronounced in giants than in dwarfs of the same spectral type.