Probing non polar interstellar molecules through their protonated form: Detection of protonated cyanogen (NCCNH+)

TL;DR

This study reports the first detection of protonated cyanogen (NCCNH+) in interstellar clouds, providing insights into the chemistry of non-polar molecules like cyanogen through their protonated forms.

Contribution

First observational evidence of cyanogen in space via its protonated form, expanding understanding of non-polar molecule detection in interstellar media.

Findings

Detected NCCNH+ in TMC-1 and L483 clouds.

Derived low fractional abundances of NCCNH+ relative to H2.

Predicted cyanogen abundance comparable to other nitriles.

Abstract

Cyanogen (NCCN) is the simplest member of the series of dicyanopolyynes. It has been hypothesized that this family of molecules can be important constituents of interstellar and circumstellar media, although the lack of a permanent electric dipole moment prevents its detection through radioastronomical techniques. Here we present the first solid evidence of the presence of cyanogen in interstellar clouds through the detection of its protonated form toward the cold dark clouds TMC-1 and L483. Protonated cyanogen (NCCNH+) has been identified through the J=5-4 and J=10-9 rotational transitions using the 40m radiotelescope of Yebes and the IRAM 30m telescope. We derive beam averaged column densities for NCCNH+ of (8.6+/-4.4)e10 cm-2 in TMC-1 and (3.9+/-1.8)e10 cm-2 in L483, which translate to fairly low fractional abundances relative to H2, in the range (1-10)e-12. The chemistry of protonated molecules in dark clouds is discussed, and it is found that, in general terms, the abundance ratio between the protonated and non protonated forms of a molecule increases with increasing proton affinity. Our chemical model predicts an abundance ratio NCCNH+/NCCN of 1e-4, which implies that the abundance of cyanogen in dark clouds could be as high as (1-10)e-8 relative to H2, i.e., comparable to that of other abundant nitriles such as HCN, HNC, and HC3N.