Pure hydrocarbon cycles in TMC-1: Discovery of ethynyl cyclopropenylidene, cyclopentadiene, and indene

We report the detection for first time in space of three new pure hydrocarbon cycles TMC-1: c -C 3 HCCH (ethynyl cyclopropenylidene), 5 H 6 (cyclopentadiene), and 9 8 (indene). derive a column density 3.1 × 10 11 cm −2 cycle similar values, range (1−2) 13 , second third. This means that cyclopentadiene indene, spite their large size, are exceptionally abundant, only factor five less abundant than ubiquitous cyclic 2 . The high abundance found these two together with previously propargyl radical (CH CCH) other hydrocarbons, such as vinyl allenyl acetylene (Agúndez et al. 2021, A&A, 647, L10; Cernicharo 2021a, L2; 2021b, L3), start to allow us quantify content rings cold dark clouds identify intermediate species probably behind situ bottom-up synthesis aromatic environments. While is most likely formed through reaction between CCH observed abundances indene difficult explain currently proposed chemical mechanisms. Further studies needed how five- six-membered under conditions cloud TMC-1.