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

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 NCnS (n ≥ 4) and HCnS (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.