Cumulene carbenes in TMC-1: Astronomical discovery of l-H2C5 ★.
We report the first detection in space of the cumulene carbon chain l-H2C5. A total of eleven rotational transitions, with J = 7-10 and K = 0 and 1, were detected in TMC-1 in the 31.0-50.4 GHz range using the Yebes 40m radio telescope. We derive a column density of (1.8±0.5)×1010 cm-2. In addition, we report observations of other cumulene carbenes detected previously in TMC-1, to compare their abundances with the newly detected cumulene carbene chain. We find that l-H2C5 is ~4.0 times less abundant than the larger cumulene carbene l-H2C6, while it is ~300 and ~500 times less abundant than the shorter chains l-H2C3 and l-H2C4. 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  H2 isomers with n > 3.
['Cabezas|C|C|', 'Tercero|B|B|', 'Agúndez|M|M|', 'Marcelino|N|N|', 'Pardo|J R|JR|', 'de Vicente|P|P|', 'Cernicharo|J|J|']
Astrochemistry ISM: individual (TMC-1) ISM: molecules line: identification molecular data