August 2005


Cyclopropenylidene (c-C3H2) was first identified by Thaddeus et at. (see also here) in 1985 in various sources, including Orion A and in diffuse molecular clouds. In spite of its unusual nature, this species is widely observed and more thoroughly confirmed than many other astromolecules. Two isotopic variants have also been observed, including monodeuterated c-C3HD by Bell et al. and the mass 13 isotope of C by Gomez-Gonzalez et al. and Madden et al. It has also been observed in extragalactic sources, including NGC 5128 by Seaquist & Bell and NGC 253 and M82 by Tomoko et al.

UPDATE (July 2018): Cyclopropenylidene was detected in the protoplanetary disk HD 163296 by Qi et al. in 2013.

The ground electronic state of cyclopropenylidene is a singlet. There is also a triplet state which is somewhat higher in energy. Both forms are examples of carbenes, species that possess a carbon with only two bonds instead of the usual four. Methylene (CH2) is the prototypical carbene. They tend to be very reactive. Hence, cyclopropenylidene is thought to be a precursor for various other astromolecules.

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