Discovery of two new interstellar molecules with QUIJOTE: HCCCHCCC and HCCCCS
R. Fuentetaja, M. Agúndez, C. Cabezas, B. Tercero, N. Marcelino, J. R. Pardo, P. de Vicente, J. Cernicharo
Abstract
We report on the discovery of two new molecules, HCCCHCCC and HCCCCS, towards the starless core TMC-1 in the Taurus region from the QUIJOTE line survey in the 31.1–50.2 GHz frequency range. We identify a total of twenty-nine lines of HCCCHCCC and six rotational transitions of HCCCCS. The rotational quantum numbers range from J u = 10 up to 15 and K a ≤ 2 for HCCCHCCC and J u = 21/2 up to 31/2 for HCCCCS. We derived a column density for HCCCHCCC of N = (1.3±0.2) × 10 11 cm −2 with a rotational temperature of 6±1 K, while for HCCCCS we derived N = (9.5±0.8) × 10 10 cm −2 and T rot = 10±1 K. The abundance of HCCCHCCC is higher than that of its recently discovered isomer, l-H 2 C 6 . If we compare HCCCCS with its related molecules, HCS and HCCS, we obtain abundance ratios HCS/HCCCCS = 58 and HCCS/HCCCCS = 7.2. We investigated the formation of these two molecules using chemical modelling calculations. The observed abundances can be accounted for by assuming standard gas-phase formation routes involving neutral-neutral reactions and ion-neutral reactions.