Wikipedia
Methylidenecarbene
Methylidenecarbene (systematically named λ-ethene and dihydrido-1κH-dicarbon(C—C)) is an organic compound with the chemical formula (also written [] or ). It is a metastable proton tautomer of acetylene, which only persists as an adduct. It is a colourless gas that phosphoresces in the far-infrared range. It is the simplest unsaturated carbene.