A new protonated molecule discovered in TMC-1: HCCNCH⁺

In recent years we have seen an important increase in the number of protonated molecules detected cold dense clouds. Here report detection TMC-1 HCCNCH+, form HCCNC, which is a metastable isomer HC3N. This first cloud. The was based on observations carried out with Yebes 40m and IRAM 30m telescopes, revealed four harmonically related lines. We derive rotational constant B = 4664.431891 +/- 0.000692 MHz centrifugal distortion D 519.14 4.14 Hz. From high-level ab initio screening potential carriers confidently assign series lines to ion HCCNCH+. column density (3.0 0.5)e10 cm-2 for results HCCNCH+/HCCNC abundance ratio 0.010 0.002. value well reproduced by state-of-the-art chemical model, however subject uncertainties regarding chemistry observational theoretical status clouds indicate that there exists global trend protonated-to-neutral ratios MH+/M increasing proton affinity neutral M, although if one restricts species M high affinities (>700 kJ/mol), fall range 0.001-0.1, no apparent correlation affinity. suggest various are good candidates near future.