Discovery of Interstellar Isocyanogen (CNCN): Further Evidence that Dicyanopolyynes Are Abundant in Space*

It is thought that dicyanopolyynes could potentially be abundant interstellar molecules; though, their lack of a dipole moment makes it impossible to detect them through radioastronomical techniques. Recently, the simplest member of this chemical family, cyanogen (NCCN), was indirectly probed for the first time in interstellar space through the detection of its protonated form toward the dense clouds L483 and TMC-1. Here we present a second set of firm evidence indicating the presence of NCCN in interstellar space, namely the detection of the metastable and polar isomer isocyanogen (CNCN). This species has been identified in L483 and tentatively in TMC-1 by observing various rotational transitions in the λ 3 mm band with the IRAM 30 m telescope. We derive beam-averaged column densities for CNCN of 1.6 × 10 12 cm −2 in L483 and 9 × 10 11 cm −2 in TMC-1, which imply fractional abundances relative to H 2 in the range of (5–9) × 10 −11 . While the presence of NCCN in interstellar clouds seems undoubtable due to the detection of NCCNH + and CNCN, putting tight constraints on its abundance is still hampered by the poor knowledge of the chemistry that links NCCN with NCCNH + and especially with CNCN. We estimate that NCCN could be fairly abundant, in the range of 10 −9 –10 −7 relative to H 2 , such as other abundant nitriles like HCN and HC 3 N.