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In the Wikipedia article of Cyclopropenylidene, it says:

The major formation reaction of c-C3H2 is the dissociative recombination of c-C3H3+.

C3H3+ + e− → C3H2 + H

c-C3H3+ is a product of a long chain of carbon chemistry that occurs in the ISM.

From that, I conclude that Cyclopropenylidene in the ISM (interstellar medium) is also a product of a long chain of carbon chemistry.

Question: What "long chain of carbon chemistry" in the interstellar medium produces cyclopropenylidene (C3H2)?

Note: While Detection of Cyclopropenylidene on Titan with ALMA is interesting news, my question is about the ISM, not (necessarily at least) Titan's upper atmosphere.

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  • $\begingroup$ Well indeed the Wikipedia article just shift the "problem" of formation from the carbene to the conjugated cation. Perhaps you can try posting on Chemistry SE. $\endgroup$
    – Alchimista
    Commented Oct 29, 2020 at 8:51
  • $\begingroup$ @Alchimista those knowledgable about, and how to research about conditions in the interstellar medium are more likely to see this question here than there. I did post a link to this question in chat there earlier. $\endgroup$
    – uhoh
    Commented Oct 29, 2020 at 11:14
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    $\begingroup$ You might find refs in this paper ncbi.nlm.nih.gov/pmc/articles/PMC2982172/#!po=2.23881 The paper itself is more on the influx of molecules to Earth but in the intro mentions C chemistry in ISM. $\endgroup$
    – Alchimista
    Commented Oct 29, 2020 at 11:52
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    $\begingroup$ articles.adsabs.harvard.edu/pdf/1990A%26A...239..319M $\endgroup$
    – Mithoron
    Commented Oct 29, 2020 at 15:07

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The quote from Wikipedia further reads:

Carbon insertion reactions are crucial in this chain for forming C3H3+. However, as for most ion-molecule reactions speculated to be important in interstellar environments, this pathway has not been verified by laboratory studies.

It is hard to speculate the pathway to the formation of C3H2. The most common pathway known is electronic Dissociative Recombination (EDR) pathway between C3Hx (more details in ref.1).

After digging, I found a possible pathway involving molecules with more than 3 carbon atoms(ref.2):

Astronomical evolution mechanism of small size polycyclic aromatic hydrocarbon (PAH) was analyzed using the first principles quantum-chemical calculation. Starting model molecule was benzene (C6H6), which would be transformed to (C5H5) due to carbon void created by interstellar high speed proton attack. In a protoplanetary disk around a young star, molecules would be illuminated by high energy photon and ionized to be cationic-(C5H5). Calculation shows that from neutral to tri-cation, molecule keeps original configuration. At a step of sixth cation, there occurs surprising creation of cyclic-C3H2, which is the smallest PAH. Astronomical cyclic-C3H2 had been identified by radio astronomy. Deep photoionization of cyclic-C3H2 brings successive molecular change. Neutral and mono-cation keep cyclic configuration. At a step of di-cation, molecule was transformed to aliphatic chain-C3H2. Finally, chain-C3H2 was decomposed to pure carbon chain-C3 and two hydrogen atoms.

References:

  1. Loison, Jean-Christophe & Agúndez, Marcelino & Wakelam, Valentine & Roueff, Evelyne & Gratier, Pierre & Marcelino, Nain & Reyes, Dianailys & Cernicharo, Josee & Gerin, Marion. (2017). The interstellar chemistry of C3H and C3H2 isomers. Monthly notices of the Royal Astronomical Society. 470. 10.1093/mnras/stx1265.
  2. Norio Ota, Astronomical Creation of Cyclic-C3H2 and Chain-C3 Due to Interstellar Deep Photoionization, DOI: arxiv.org/abs/1810.06006
  3. Cox, P., Guesten, R., and Henkel, C., Observations of C3H2 in the diffuse interstellar medium., Astronomy and Astrophysics, vol. 206, pp. 108–116, 1988 (Link).
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