Letter to the Editor

Study of the HCCNC and HNCCC isotopologs in TMC-1^⋆

¹ Dept. de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), C/ Serrano 121, 28006 Madrid, Spain
e-mail: jose.cernicharo@csic.es; carlos.cabezas@csic.es
² Observatorio Astronómico Nacional (OAN, IGN), C/ Alfonso XII, 3, 28014 Madrid, Spain
³ Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain
⁴ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, 92190 Meudon, France

Received: 1 December 2023
Accepted: 22 January 2024

Abstract

We present the detection of the three ¹³C isotopologs of HCCNC and HNCCC toward TMC-1 using the QUIJOTE line survey. In addition, the D species has also been detected for these two isomers of HCCCN, whereas the ¹⁵N isotopolog was only detected for HCCNC. Using high-J lines of HCCNC and HNCCC, we were able to derive very precise rotational temperatures, column densities, and subsequently the isotopic abundance ratios. We found that ¹²C/¹³C is ∼90 for the three possible substitutions in both isomers. These results are slightly different from what has been found for the most abundant isomer HCCCN, for which abundances of 105, 95, and 66 were found for each one of the three possible positions of ¹³C. The H/D abundance ratio was found to be 31 ± 4 for HCCNC and of 53 ± 6 for HNCCC. The latter is similar to the H/D abundance ratio derived for HCCCN (∼59). The ¹⁴N/¹⁵N isotopic abundance ratio in HCCNC is 243 ± 24.