dicarbon

Dicarbon, with chemical formula C2, is a diatomic molecule consisting of two carbon atoms. It is an elementary species of carbon that occurs under specialized, high-energy conditions such as flames, carbon vapors, plasmas, or other high-temperature environments. In ordinary ambient conditions, elemental carbon exists as graphite or diamond rather than as diatomic C2.

Bonding and structure: C2 is a homonuclear diatomic molecule connected by a strong covalent bond. In simple molecular orbital descriptions, the bond order is commonly taken as two, arising from sigma and pi bonding interactions. The bond length in the gas phase is about 1.27 Å, and the dissociation energy is roughly 600 kJ/mol. The precise electronic structure of C2 is a subject of ongoing theoretical study, with multi-reference considerations highlighting complex electron correlation and resonance effects. Nevertheless, C2 is regarded as a short, relatively robust bond in the contexts in which it is observed.

Occurrence and spectroscopy: C2 has been detected in various high-energy environments, including combustion flames, carbon vapors, and laboratory plasmas. In astrophysics and planetary science, C2 features appear in the spectra of certain stars, comets, and interstellar regions, most famously via electronic transitions known as the Swan bands. These spectral signatures enable identification and study of C2 in environments where it is transient.

Production and use: C2 is typically generated in situ in laboratory settings, for example by laser ablation of graphite or by pyrolysis of hydrocarbons at high temperature. It serves as a valuable subject for fundamental studies of chemical bonding, spectroscopy, and reaction dynamics, rather than as a bulk reagent.

Properties and notes: The molecule has a molecular weight of 24.02 g/mol and a zero dipole moment. It is a reactive, non-stable species outside of high-energy environments and is principally of interest for research into carbon bonding and gas-phase chemistry.