09-07-2021-1346 - Diacetylene (also known as butadiyne) ethynyl radical λ3-ethyne and hydridodicarbon(C—C))

 Diacetylene (also known as butadiyne) is the organic compound with the formula C₄H₂. It is the simplest compound containing two triple bonds. It is first in the series of polyynes, which are of theoretical but not of practical interest.

https://en.wikipedia.org/wiki/Diacetylene

The ethynyl radical (systematically named λ³-ethyne and hydridodicarbon(C—C)) is an organic compound with the chemical formula C≡CH (also written [CCH] or C
2H). It is a simple molecule that does not occur naturally on Earth but is abundant in the interstellar medium. It was first observed by electron spin resonance isolated in a solid argon matrix at liquid helium temperatures in 1963 by Cochran and coworkers at the Johns Hopkins Applied Physics Laboratory.^[1] It was first observed in the gas phase by Tucker and coworkers in November 1973 toward the Orion Nebula, using the NRAO 11-meter radio telescope.^[2] It has since been detected in a large variety of interstellar environments, including dense molecular clouds, bok globules, star forming regions, the shells around carbon-rich evolved stars, and even in other galaxies.

Finally, high-spectral-resolution observations of Zeeman splitting in C₂H can give information about the magnetic fields in dense clouds, which can augment similar observations that are more commonly done in the simpler cyanide (CN).^[7]

Formation and destruction[edit]

The formation and destruction mechanisms of the ethynyl radical vary widely with its environment. The mechanisms listed below represent the current (as of 2008) understanding, but other formation and destruction pathways may be possible, or even dominant, in certain situations.

Formation[edit]

In the laboratory, C₂H can be made via photolysis of acetylene (C₂H₂) or C₂HCF₃,^[8] or in a glow discharge of a mixture of acetylene and helium.^[9] In the envelopes of carbon-rich evolved stars, acetylene is created in the thermal equilibrium in the stellar photosphere. Ethynyl is created as a photodissociation product of the acetylene that is ejected (via strong stellar winds) into the outer envelope of these stars. In the cold, dense cores of molecular clouds (prior to star formation) where n > 10⁴ cm⁻³ and T < 20 K, ethynyl is dominantly formed via an electron recombination with the vinyl radical (C
2H+
3).^[10] The neutral-neutral reaction of propynylidyne (C₃H) and atomic oxygen also produces ethynyl (and carbon monoxide, CO), though this is typically not a dominant formation mechanism. The dominant creation reactions are listed below.

• C
  2H+
  3 + e⁻ → C₂H + H + H
• C
  2H+
  3 + e⁻ → C₂H + H₂
• CH₃CCH⁺ + e⁻ → C₂H + CH₃
• C₃H + O → C₂H + CO

Destruction[edit]

The destruction of ethynyl is dominantly through neutral-neutral reactions with O₂ (producing carbon monoxide and formyl, HCO), or with atomic nitrogen (producing atomic hydrogen and C₂N). Ion-neutral reactions can also play a role in the destruction of ethynyl, through reactions with HCO⁺ and H+
3. The dominant destruction reactions are listed below.

• C₂H + O₂ → HCO + CO
• C₂H + N → C₂N + H
• C₂H + HCO⁺ → C
  2H+
  2 + CO
• C₂H + H+
  3 → C
  2H+
  2 + H₂

https://en.wikipedia.org/wiki/Ethynyl_radical

In astronomy, Bok globules are isolated and relatively small dark nebulae, containing dense cosmic dust and gas from which star formation may take place. Bok globules are found within H II regions, and typically have a mass of about 2^[1] to 50 solar masses contained within a region about a light year or so across (about 4.5×10⁴⁷ m³).^[2] They contain molecular hydrogen (H₂), carbon oxides and helium, and around 1% (by mass) silicate dust. Bok globules most commonly result in the formation of double- or multiple-star systems.^[3]

https://en.wikipedia.org/wiki/Bok_globule