2020A&A...642L..17C

Using the Yebes 40m and IRAM 30m radio telescopes, we detected a series of harmonically related lines with a rotational constant B₀=4460.590±0.001MHz and a distortion constant D₀=0.511±0.005kHz towards the cold dense core TMC-1. High-level-of-theory ab initio calculations indicate that the best possible candidate is protonated tricarbon monoxide, HC₃O⁺. We have succeeded in producing this species in the laboratory and observed its J_u-J_l=2-1 and 3-2 rotational transitions. Hence, we report the discovery of HC₃O⁺ in space based on our observations, theoretical calculations, and laboratory experiments. We derive an abundance ratio N(C₃O)/N(HC₃O⁺)∼7. The high abundance of the protonated form of C₃O is due to the high proton affinity of the neutral species. The chemistry of O-bearing species is modelled, and predictions are compared to the derived abundances from our data for the most prominent O-bearing species in TMC-1.