The radical C3H can exist in either a linear form (l-C3H) or as a tricarbon ring with the attached hydrogen atom (c-C3H). Both isomers have been detected at millimeter wavelengths in the interstellar medium and in the envelopes of evolved stars. C3H is an important intermediary in the production of heavier species of the form CnH (n > 3), which have been detected astronomically for n = 4–8. The linear propynylidynium ion, C3H+, has also been reported in the interstellar medium (Pety et al. 2012).