The ethynyl radical (C₂H) was discovered in 1974 by Tucker et al. toward Orion and other sources with the NRAO 36 foot radio telescope. The detection of two additional hyperfine components were added to the original four lines by Tucker & Kuttner in 1978. All of these features are associate with the N=1-0 transition; in 1982, Ziurys et al. reported the detections of five of the hyperfine components of the N=3-2 transition. The deuterated species C₂D was detectd by Combes et al. in 1985. Extragalactic detections of ethynyl radical include a report from 1988 by Henkel et al. toward M82 (the Cigar galaxy) and in 2001 by Nakajima et al. toward NGC 1068 and NGC 253.

While low temperature astrochemistry is dominated by ion-molecule reactions, species like ethynyl and cyano radicals can also react with no barrier with some unsaturated molecules lke acetylene and ethylene.