Abstract
We report the detection in TMC-1 of the protonated form of C(3)S. The discovery of the cation HC(3)S(+) was carried through the observation of four harmonically related lines in the Q band using the Yebes 40m radiotelescope, and is supported by accurate ab initio calculations and laboratory measurements of its rotational spectrum. We derive a column density N(HC(3)S(+)) = (2.0 ± 0.5) × 10(11) cm(-2), which translates to an abundance ratio C(3)S/HC(3)S(+) of 65 ± 20. This ratio is comparable to the CS/HCS(+) ratio (35 ± 8) and is a factor of about ten larger than the C(3)O/HC(3)O(+) ratio previously found in the same source. However, the abundance ratio HC(3)O(+)/HC(3)S(+) is 1.0 ± 0.5, while C(3)O/C(3)S is just ~ 0.11. We also searched for protonated C(2)S in TMC-1, based on ab initio calculations of its spectroscopic parameters, and derive a 3σ upper limit of N(HC(2)S(+))≤ 9×10(11) cm(-2) and a C(2)S/HC(2)S(+) ≥ 60. The observational results are compared with a state-of-the-art gas-phase chemical model and conclude that HC(3)S(+) is mostly formed through several pathways: proton transfer to C(3)S, reaction of S(+) with c-C(3)H(2), and reaction between neutral atomic sulfur and the ion C(3)H(+) (3).