Discovery of interstellar NC₄NH⁺: Dicyanopolyynes are indeed abundant in space

The previous detection of two species related to the nonpolar molecule cyanogen (NCCN), its protonated form (NCCNH + ) and one metastable isomer (CNCN), in cold dense clouds supported hypothesis that dicyanopolyynes are abundant space. Here we report first identification space NC 4 NH . This cation is N, which second member series after NCCN. was based on observation six harmonically lines within Yebes 40m line survey TMC-1 QUIJOTE. can be fitted a rotational constant B = 1293.90840 ± 0.00060 MHz centrifugal distortion D 28.59 1.21 Hz. We confidently assign this high-level ab initio calculations, supports HC 5 from with 2 lower than derived here. column density (1.1 ?0.6 +1.4 × 10 cm ?2 , implies eight times less NCCNH CNCN, previously reported toward L483 tentatively TMC-1, confirmed latter source. estimate NCCN N present abundances few order magnitude 3 respectively. means NC?(CC) n ?CN at level corresponding monocyanopolyynes HCC?(CC) ?CN. reactions radicals CN C HNC arise as most likely formation pathways clouds.