A study of C<sub>4</sub>H<sub>3</sub>N isomers in TMC-1: Line by line detection of HCCCH<sub>2</sub>CN
N. Marcelino, B. Tercero, M. Agúndez, J. Cernicharo
Abstract
We present Yebes 40 m telescope observations of the three most stable C 4 H 3 N isomers towards the cyanopolyyne peak of TMC-1. We have detected 13 transitions from CH 3 C 3 N (A and E species), 16 lines from CH 2 CCHCN, and 27 lines ( a -type and b -type) from HCCCH 2 CN. We thus provide a robust confirmation of the detection of HCCCH 2 CN and CH 2 CCHCN in space. We have constructed rotational diagrams for the three species and obtained rotational temperatures between 4 and 8 K as well as similar column densities for the three isomers, in the range (1.5−3) × 10 12 cm −2 . Our chemical model provides abundances of the order of the observed ones, although it overestimates the abundance of CH 3 CCCN and underestimates that of HCCCH 2 CN. The similarity of the observed abundances of the three isomers suggests a common origin, most probably involving reactions of the radical CN with the unsaturated hydrocarbons methyl acetylene and allene. Studies of reaction kinetics at low temperatures and further observations of these molecules in different astronomical sources are needed to draw a clear picture of the chemistry of C 4 H 3 N isomers in space.