Letter to the Editor

Discovery of H₂CCCH⁺ in TMC-1^⋆

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
e-mail: asvany@ph1.uni-koeln.de
² Dept. de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), Serrano 121, 28006 Madrid, Spain
³ Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain
⁴ Observatorio Astronómico Nacional (OAN, IGN), Madrid, Spain
⁵ Institut des Sciences Moléculaires (ISM), CNRS, Univ. Bordeaux, 351 cours de la Libération, 33400 Talence, France
⁶ Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁷ , Serrano 123, 28006 Madrid, Spain

Received: 13 June 2023
Accepted: 3 July 2023

Abstract

Based on a novel laboratory method, 14 millimeter-wave lines of the molecular ion H₂CCCH⁺ have been measured in high resolution, and the spectroscopic constants of this asymmetric rotor determined with high accuracy. Using the Yebes 40 m and IRAM 30 m radio telescopes, we detected four lines of H₂CCCH⁺ toward the cold dense core TMC-1. With a dipole moment of about 0.55 D obtained from high-level ab initio calculations, we derive a column density of 5.4±1×10¹¹ cm⁻² and 1.6±0.5×10¹¹ cm⁻² for the ortho and para species, respectively, and an abundance ratio N(H₂CCC)/N(H₂CCCH⁺) = 2.8±0.7. The chemistry of H₂CCCH⁺ is modeled using the most recent chemical network for the reactions involving the formation of H₂CCCH⁺. We find a reasonable agreement between model predictions and observations, and new insights into the chemistry of C₃-bearing species in TMC-1 were obtained.