2022A&A...663L...3F

Using the QUIJOTE line survey in the 32.0-50.4 GHz range, we report the discovery of the molecule CH₂CCHC₄H towards the prestellar cold core TMC-1 in the Taurus region. We also present a rigorous detection of CH₂CCHC₃N, along with its detailed analysis. We identified a total of twenty rotational transitions for each one of these molecules. The rotational quantum numbers range from J_u = 17 up to 24 and K_a≤ 3. The column density for CH₂CCHC₄H is N = (2.2 ± 0.2) x 10¹² cm^–2, while for CH₂CCHC₃N, we derived N = (1.2 ± 0.15) x 10¹¹ cm^–2. The rotational temperature is 9.0 ± 0.5 K for both species. The abundance ratiobetween CH₂CCHC₄H and CH₂CCHC₃N is 18 ± 4. We also compared the column densities of these species with those of their isomers CH₃C₆H and CH₃C₅N, derived from their J = 20 - 10 up to J = 31 - 30 rotational transitions observed with the QUIJOTE line survey. The observed abundances for all these species are reasonably well explained by state-of-the-art chemical models of TMC-1. The observed astronomical frequencies were merged with laboratory frequencies from the literature to derive improved spectroscopic parameters.