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

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 by 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 40 m radiotelescope of Yebes and the IRAM 30 m telescope. We derive beam-averaged column densities for NCCNH + of (8.6 ± 4.4) × 10 10 cm −2 in TMC-1 and (3.9 ± 1.8) × 10 10 cm −2 in L483, which translate into fairly low fractional abundances relative to H 2 , in the range (1-10) × 10 −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 ∼10 −4 , which implies that the abundance of cyanogen in dark clouds could be as high as (1-10) × 10 −8 relative to H 2 , i.e., comparable to that of other abundant nitriles such as HCN, HNC, and HC 3 N.

Detection of the HC3NH+ and HCNH+ ions in the L1544 pre-stellar core

“…(ii) Formation (or destruction) routes for HCNH + and HC 3 NH + must be added to the chemical network. Agúndez et al (2015) also came to this conclusion in their study of the ion NCCNH + in the cold dark clouds TMC-1 and L483. In Figure 6.…”

Abundant Z-cyanomethanimine in the interstellar medium: paving the way to the synthesis of adenine

“…Our analysis yielded a fractional molecular abundance of 1.4×10 −12 for this species (Table 2). If we assume a [NCCNH + ]/[NCCN] ratio of ∼10 −4 as inferred from the chemical modelling of Agúndez et al (2015), the abundance of NCCN would be 1.4×10 −8 cm −2 .…”

Chemical modelling of complex organic molecules with peptide-like bonds in star-forming regions

“…Indeed, Eshchenko et al (2002) and Glarborg et al (1998) have shown that the HCCO + NO HCNO + CO could be an important pathway to form or destroy HCNO. The recent detection of unexpected high abundances of HCCO toward cold dark clouds (Agúndez et al 2015) favours this idea. Glarborg et al (1998) also suggested that HCNO could be efficiently recycled to NO through the reaction with OH.…”