Discovery of interstellar isocyanogen (CNCN): further evidence that dicyanopolyynes are abundant in space

TL;DR

This study provides the first firm detection of interstellar isocyanogen (CNCN), supporting the idea that dicyanopolyynes are common in space, and offers new insights into their abundance and chemical relationships.

Contribution

First detection of interstellar isocyanogen (CNCN) via rotational transitions, confirming the presence of cyanogen derivatives in space and expanding understanding of interstellar nitrile chemistry.

Findings

CNCN detected in L483 and tentatively in TMC-1.

Column densities of CNCN estimated at 1.6e12 and 9e11 cm-2.

NCCN could be fairly abundant, with estimated relative abundance 1e-9 to 1e-7.

Abstract

It is thought that dicyanopolyynes could be potentially abundant interstellar molecules, although their lack of 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 firm evidence of 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 3 mm band with the IRAM 30m telescope. We derive beam-averaged column densities for CNCN of 1.6e12 cm-2 in L483 and 9e11 cm-2 in TMC-1, which imply fractional abundances relative to H2 in the range (5-9)e-11. While the presence of NCCN in interstellar clouds seems out of doubt owing 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 1e-9 - 1e-7 relative to H2, as other abundant nitriles like HCN and HC3N.