Authors: Cabezas, C.; Agundez, M.; Marcelino, N.; Tercero, B.; Fuentetaja, R.; de Vicente, P.; Cernicharo, J.

Journal: ASTRONOMY & ASTROPHYSICS

Publication date: 2022/03/23

DOI: 10.1051/0004-6361/202142972

Abstract: We report the detection of the protonated form of HC7N in TMC-1. The discovery of the cation HC7NH+ was carried out via the observation of nine harmonically related lines in the Q-band using the Yebes 40 m radiotelescope. The observed frequencies allowed us to obtain the rotational constants B-0 = 553.938802 (160) MHz and D-0 = 3.6292 (705) Hz. The identification of HC7NH+ is further supported by accurate ab initio calculations. We derived a column density of (5.5 +/- 0.7) x 10(10) cm(-2), which constitutes another piece of evidence for the identification of the carrier. In addition, we revised the HC7N column density and we derived a new value of (2.1 +/- 0.2) x 10(13) cm(-2). Hence, the abundance ratio HC7N/HC7NH+ is similar to 380, while those for HC3N/HC3NH+ and HC5N/HC5NH+ are similar to 230 and similar to 240, respectively. Here, we discuss these results within the framework of a chemical model for protonated molecules in cold dense clouds.