Cumulene carbenes in TMC-1: Astronomical discovery of <i>l</i>-H<sub>2</sub>C<sub>5</sub>
C. Cabezas, B. Tercero, M. Agúndez, N. Marcelino, J. R. Pardo, P. de Vicente, J. Cernicharo
Abstract
We report the first detection in space of the cumulene carbon chain l -H 2 C 5 . A total of eleven rotational transitions, with J up = 7−10 and K a = 0 and 1, were detected in TMC-1 in the 31.0–50.4 GHz range using the Yebes 40 m radio telescope. We derived a column density of (1.8 ± 0.5)×10 10 cm −2 . In addition, we report observations of other cumulene carbenes detected previously in TMC-1 in order to compare their abundances with the newly detected cumulene carbene chain. We find that l -H 2 C 5 is ∼4.0 times less abundant than the larger cumulene carbene l -H 2 C 6 , while it is ∼300 and ∼500 times less abundant than the shorter chains l -H 2 C 3 and l -H 2 C 4 . We discuss the most likely gas-phase chemical routes to these cumulenes in TMC-1 and stress that chemical kinetics studies able to distinguish between different isomers are needed to shed light on the chemistry of C n H 2 isomers with n > 3.