| Abstract
| - We report the detection of the protonated form of HC 7N in TMC-1. The discovery of the cation HC 7NH + 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 B0 = 553.938802 (160) MHz and D0 = 3.6292 (705) Hz. The identification of HC 7NH + is further supported by accurate ab initio calculations. We derived a column density of (5.5 ± 0.7) × 10 10 cm −2, which constitutes another piece of evidence for the identification of the carrier. In addition, we revised the HC 7N column density and we derived a new value of (2.1 ± 0.2) × 10 13 cm −2. Hence, the abundance ratio HC 7N/HC 7NH + is ∼380, while those for HC 3N/HC 3NH + and HC 5N/HC 5NH + are ∼230 and ∼240, respectively. Here, we discuss these results within the framework of a chemical model for protonated molecules in cold dense clouds.
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