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.

First, the relative abundance of ethynyl is an indication of the carbon-richness of its environment (as opposed to oxygen, which provides an important destruction mechanism).

[5] Acetylene (C2H2) does not have a dipole moment, and therefore pure rotational transitions (typically occurring in the microwave region of the spectrum) are too weak to be observable.

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 (C2H+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.

In its ground electronic and vibrational state, the nuclei are collinear, and the molecule has a permanent dipole moment estimated to be μ = 0.8 D = 2.7×10−30 C·m.