SIMBAD references

Using the Yebes 40m radio telescope, we report the detection of a series of seven lines harmonically related with a rotational constant B₀=1295.81581±0.00026MHz and a distortion constant D₀=27.3±0.5Hz towards the cold dense cloud TMC-1. Ab initio calculations indicate that the best possible candidates are the cations HC₅NH⁺ and NC₄NH⁺. From a comparison between calculated and observed rotational constants and other arguments based on proton affinities and dipole moments, we conclude that the best candidate for a carrier of the observed lines is the protonated cyanodiacetylene cation, HC₅NH⁺. The HC₅N/HC₅NH⁺ ratio derived in TMC-1 is 240, which is very similar to the HC₃N/HC₃NH⁺ ratio. Results are discussed in the framework of a chemical model for protonated molecules in cold dense clouds.