Tentative detection of HC<sub>5</sub>NH<sup>+</sup> in TMC-1
N. Marcelino, M. Agúndez, B. Tercero, C. Cabezas, C. Bermúdez, J. D. Gallego, P. deVicente, J. Cernicharo
Abstract
Using the Yebes 40m radio telescope, we report the detection of a series of seven lines harmonically related with a rotational constant B 0 = 1295.81581 ± 0.00026MHz and a distortion constant D 0 = 27.3 ± 0.5Hz towards the cold dense cloud TMC-1. Ab initio calculations indicate that the best possible candidates are the cations HC 5 NH + and NC 4 NH + . 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, HC 5 NH + . The HC 5 N/HC 5 NH + ratio derived in TMC-1 is 240, which is very similar to the HC 3 N/HC 3 NH + ratio. Results are discussed in the framework of a chemical model for protonated molecules in cold dense clouds.