Discovery of C<sub>5</sub>H<sup>+</sup> and detection of C<sub>3</sub>H<sup>+</sup> in TMC-1 with the QUIJOTE line survey
J. Cernicharo, M. Agúndez, C. Cabezas, R. Fuentetaja, B. Tercero, N. Marcelino, Yasuki Endo, J. R. Pardo, P. de Vicente
Abstract
We report the discovery of the C 5 H + cation toward TMC-1 with the QUIJOTE line survey. Four lines from J = 7 − 6 up to J = 10 − 9 have been identified in perfect harmonic frequency relation that can be fit with B = 2411.94397 ± 0.00055 MHz and D = 138 ± 3 Hz. The standard deviation of the fit is 4.4 kHz. After discarding potential candidates, C 5 H − among them, we conclude that the carrier is C 5 H + , for which accurate ab initio calculations provide B = 2410.3 MHz. We also report for the first time in a cold starless core the detection of the C 3 H + cation. The column densities we derive for C 5 H + and C 3 H + are (8.8 ± 0.5)×10 10 cm −2 and (2.4 ± 0.2)×10 10 cm −2 , respectively. Hence, the C 5 H + /C 3 H + abundance ratio is 3.7 ± 0.5. The fact that C 5 H + is more abundant than C 3 H + is well explained by dedicated chemical models and is due to the slow reactivity of C 5 H + with H 2 , while C 3 H + reacts with H 2 .