Molecular Carbon Chains and Rings in TMC‐1

We present mapping results in several rotational transitions of HC 3 N, C 6 H, both cyclic and linear C 3 H 2 and C 3 H, 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 H 2 CCC (hereafter l -C 3 H 2 ) is found to deviate significantly from the distributions of the cyclic isomer c -C 3 H 2 , HC 3 N, and C 6 H, which, in turn, look very similar. The cyclic over linear abundance ratio of C 3 H 2 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 C 3 H 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.