Letter to the Editor

More sulphur in TMC-1: Discovery of the NC₃S and HC₃S radicals with the QUIJOTE line survey^⋆

¹ Dept. de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), C/ Serrano 121, 28006 Madrid, Spain
e-mail: jose.cernicharo@csic.es
² Observatorio Astronómico Nacional (OAN, IGN), C/ Alfonso XII, 3, 28014 Madrid, Spain
³ Observatorio de Yebes (IGN), Cerro de la Palera s/n, 19141 Yebes, Guadalajara, Spain

Received: 25 June 2024
Accepted: 5 July 2024

Abstract

We present the detection of the free radicals NC₃S and HC₃S towards TMC-1 with the QUIJOTE line survey. The derived column densities are (1.4 ± 0.2)×10¹¹ for NC₃S and (1.5 ± 0.2)×10¹¹ for HC₃S. We searched for NCCS, but only three transitions are within the domain of our QUIJOTE line survey and the observed lines are marginally detected at the 3σ level, providing an upper limit to its column density of ≤6 × 10¹⁰ cm⁻². We also unsuccessfully searched for longer species of the NC_nS (n ≥ 4) and HC_nS (n ≥ 5) families in our TMC-1 data. A chemical model based on a reduced set of reactions involving HC₃S and NC₃S predicts abundances that are 10–100 times below the observed values. These calculations indicate that the most efficient reactions of formation of HC₃S and NC₃S in the model are S + C₃H₂ and N + HC₃S, respectively, while both radicals are very efficiently destroyed through reactions with neutral atoms.