Authors: Cabezas, C.; Agundez, M.; Marcelino, N.; Tercero, B.; Endo, Y.; Fuentetaja, R.; Pardo, J. R.; de Vicente, P.; Cernicharo, J.


Publication date: 2022/01/07

DOI: 10.1051/0004-6361/202142815

Abstract: We report the detection in TMC-1 of the cation HCCS+ ((X) over tilde (3)Sigma(-)), which is the protonated form of the widespread radical CCS. This is the first time that a protonated radical has been detected in a cold dark cloud. Twenty-six hyperfine components from twelve rotational transitions have been observed with the Yebes 40m and IRAM 30m radio telescopes. We confidently assign the characteristic rotational spectrum pattern to HCCS+ based on the good agreement between the astronomical and theoretical spectroscopic parameters. The column density of HCCS+ is (1.1 +/- 0.1) x 10(12) cm(-2), and the CCS/HCCS+ abundance ratio is 50 +/- 10, which is very similar to that of CS/HCS+ (35 +/- 8) and CCCS/HCCCS+ (65 +/- 20). From a state-of-the-art gas-phase chemical model, we conclude that HCCS+ is mostly formed by reactions of proton transfer from abundant cations such as HCO+, H3O+, and H-3(+) to the radical CCS.