===== Detection of Ethynyloxomethylium, HC3O+, in the ISM ===== J. Cernicharo, N. Marcelino, M. Agúndez, Y. Endo, C. Cabezas, C. Bermúdez, B. Tercero, and P. de Vicente\\ reported on the\\ **[[https://doi.org/10.1051/0004-6361/202039351|Discovery of HC₃O⁺ in Space: The Chemistry of O-bearing Species in TMC-1]]**\\ //Astron Astrophys.// **642**, Art. No. L17 (2020).\\ Two transitions, //J"// = 3 and 4 near 35.7 and 44.6 GHz, of a new, unknown molecule were detected in the course of a molecular line survey of the prototypical cold dark molecular cloud TMC-1 carried out with the Yebes 40 m radio telescope. Subsequently, two additional transitions, //J"// = 9 and 10 near 89.2 and 98.1 GHz, were identified in data from an older IRAM 30 m line survey of TMC-1. Laboratory measurements confirmed the identity of the molecule as ethynyloxomethylium.\\ The abundance ratio of C₃O to HC₃O⁺ is ~7, extremely low, whereas astrochemical modeling with protonation of C₃O as dominant source of HC₃O⁺ yielded a ratio of ~500 at steady state. The abundance ratio of C₃S to HC₃S⁺ should be even lower because of the larger proton affinity of C₃S compared to C₃O. However, HC₃S⁺ was not detected, and the C₃S to HC₃S⁺ ratio was evaluated to be larger than 25, strongly suggesting that protonation of C₃O is not an important source of HC₃O⁺ in TMC-1.\\ ---- Contributor(s): H. S. P. Müller 10, 2020 ----