cC3H2

cC3H2, commonly referred to as cyclopropenylidene, is the cyclic isomer of the molecular formula C3H2. It is a cyclic carbene featuring a three-membered carbon ring with a divalent carbon atom. The designation “c” signals the cyclic form, and cC3H2 is of particular interest in astrochemistry as one of the simplest cyclic hydrocarbons containing a carbene center.

The molecule has a three-membered ring structure with a reactive carbene carbon. In its ground electronic state, cC3H2 is described as a singlet carbene. Its rotational spectrum has been measured in laboratory studies, enabling reliable identification in astronomical observations.

In space, cC3H2 has been detected in several cold molecular clouds and photon-dominated regions. It serves as a useful tracer of carbon chemistry in low-temperature environments and has been observed alongside other small hydrocarbons, contributing to our understanding of chemical networks in the interstellar medium.

Formation and reactivity in astrochemical environments occur mainly via gas-phase reactions, including neutral-neutral processes and radiative associations of smaller fragments, as well as dissociative recombination of ionized precursors. As a reactive carbene, cC3H2 participates in networks that build more complex hydrocarbons and products of astrochemical evolution. It can engage with atoms and simple molecules such as atomic oxygen or nitrogen-containing species, leading to additional carbon-containing species.

Related species include the linear isomer l-C3H2, a higher-energy isomer that is also observed under certain conditions. Together, these forms illustrate constitutional isomerism in small hydrocarbon carbene systems and underscore cC3H2’s role in studies of interstellar chemistry.