2001ApJ...552..168F

We present mapping results in several rotational transitions of HC₃N, C₆H, both cyclic and linear C₃H₂ and C₃H, toward the cyanopolyyne peak of the filamentary dense cloud TMC-1 using the IRAM 30 m and MPIfR 100 m telescopes. The spatial distribution of the cumulene carbon chain propadienylidene H₂CCC (hereafter l-C₃H₂) is found to deviate significantly from the distributions of the cyclic isomer c-C₃H₂, HC₃N, and C₆H, which, in turn, look very similar. The cyclic over linear abundance ratio of C₃H₂ increases by a factor of 3 across the filament, with a value of 28 at the cyanopolyyne peak. This abundance ratio is an order of magnitude larger than the range (3-5) we observed in the diffuse interstellar medium. The cyclic over linear abundance ratio of C₃H also varies by ∼2.5 in TMC-1, reaching a maximum value (13) close to the cyanopolyyne peak. These behaviors might be related to competitive processes between ion-neutral and neutral-neutral reactions for cyclic and linear species.