Letter to the Editor

Detection of six isotopologues of CH₃CCCCH in TMC-1 with the QUIJOTE line survey

¹ Dept. de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), C/ Serrano 121, 28006 Madrid, Spain
² LUX, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, 92190 Meudon, France
³ Observatorio Astronómico Nacional (OAN, IGN), C/ Alfonso XII, 3, 28014 Madrid, Spain
⁴ Observatorio de Yebes, IGN, Cerro de la Palera s/n, 19141 Yebes, Guadalajara, Spain

^⋆ Corresponding authors: carlos.cabezas@csic.es; jose.cernicharo@csic.es

Received: 19 October 2025
Accepted: 4 November 2025

Abstract

We present the detection of the five ¹³C isotopologues and the acetylenic deuterated species of CH₃C₄H towards TMC-1 using observations from the QUIJOTE line survey taken with the Yebes 40m telescope. The identification of the CH₃C¹³CCCH and CH₃CCCCD species was based on previous laboratory spectroscopic data. In contrast, for the remaining ¹³C species, ¹³CH₃CCCCH, CH₃¹³CCCCH, CH₃CC¹³CCH, and CH₃CCC¹³CH, we carried out the spectroscopic identification directly in the QUIJOTE data. In this manner, the molecular constants derived in this work constitute the first spectroscopy information of these four species. We find that ¹²C/¹³C is 93 ± 11 for the five possible substitutions, and that the H/D abundance ratio is 54.2 ± 7.8. As previously reported, the TMC-1 gas-phase chemical model with multiply deuterated molecules accounts for the CH₃C₄H/CH₃C₄D abundance ratio calculated in this work.