Discovery of the cyclic C₅H radical in TMC-1

Cyclic C 5 H ( c -C H), the radical formed by substituting an ethynyl group CCH for hydrogen atom in 3 radical, has been detected first time space. The species is isomer of well-known linear l and ?6 kcal mol ?1 less stable. A total 17 rotational transitions were TMC-1 within 31.0–50.3 GHz range using Yebes 40m radio telescope. We derive a column density (9.0 ± 0.9) × 10 cm ?2 H. Additionally, we observed 12 lines it (1.3 0.3) , which results abundance ratio H/ 0.069. This sharp contrast with value found analogue system H, whose 5.5 TMC-1. discuss formation conclude that this probably reaction atomic carbon diacetylene.