It occurs in carbon vapor, for example in electric arcs; in comets, stellar atmospheres, and the interstellar medium; and in blue hydrocarbon flames.

The electrons in diatomic carbon are distributed among the molecular orbitals according to the Aufbau principle to produce unique quantum states, with corresponding energy levels.

[5] CASSCF calculations indicate that the quadruple bond based on molecular orbital theory is also reasonable.

In certain forms of crystalline carbon, such as diamond and graphite, a saddle point or "hump" occurs at the bond site in the charge density.

[11] C/2022 E3 (ZTF), visible in early 2023, also exhibits green color due to the presence of diatomic carbon.