Space and laboratory discovery of HC<sub>3</sub>S<sup>+</sup>
J. Cernicharo, C. Cabezas, Yasuki Endo, N. Marcelino, M. Agúndez, B. Tercero, J. D. Gallego, P. de Vicente
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 40 m 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 3 σ 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 + .