Diatomic carbon
chemical compound
Diatomic carbon (systematically named dicarbon and 1λ2,2λ2-ethene), is a green, gaseous inorganic chemical with the chemical formula C=C (also written [C2] or C2). It is kinetically unstable at ambient temperature and pressure, being removed through autopolymerisation. It occurs in carbon vapor, for example in electric arcs; in comets, stellar atmospheres, and the interstellar medium; and in blue hydrocarbon flames.
Diatomic carbon is the second simplest of the allotropes of carbon (after atomic carbon), and is an intermediate participant in the genesis of fullerenes.
Properties
C2 is a component of carbon vapor. One paper estimates that carbon vapor is around 28% diatomic, but theoretically this depends on the temperature and pressure.
Electromagnetic properties
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. The state with the lowest energy level, or ground state, is a singlet state (1Σ+g), which is systematically named ethene-1,2-diylidene or dicarbon(0•). There are several excited singlet and triplet states that are relatively close in energy to the ground state, which form significant proportions of a sample of dicarbon under ambient conditions. When most of these excited states undergo photochemical relaxation, they emit in the infrared region of the electromagnetic spectrum.
“Diatomic carbon” enters the record as chemical compound. Crown Archives preserves that source wording while asking what Diatomic, carbon and chemical can confirm, complicate or overturn.
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Datasets, specimens, observations and peer-reviewed methods provide the appropriate test for the technical claims summarized here. The source revision retrieved here is dated Sep 6, 2026. The linked authority identifier is Q866218. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “Diatomic carbon” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.