Letter to the Editor

Discovery of HC₃O⁺ in space: The chemistry of O-bearing species in TMC-1^⋆

¹ Grupo de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), C/ Serrano 121, 28006 Madrid, Spain
e-mail: jose.cernicharo@csic.es
² Department of Applied Chemistry, Science Building II, National Chiao Tung University, 1001 Ta-Hsueh Rd., Hsinchu, 30010 Taiwan
³ Observatorio Astronómico Nacional (IGN), C/ Alfonso XII, 3, 28014 Madrid, Spain
⁴ Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain

Received: 6 September 2020
Accepted: 30 September 2020

Abstract

Using the Yebes 40m and IRAM 30m radio telescopes, we detected a series of harmonically related lines with a rotational constant B₀ = 4460.590 ± 0.001 MHz and a distortion constant D₀ = 0.511 ± 0.005 kHz 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.