In 2007, the detection of the second interstellar gas phase anion -- C4H-
-- was reported by Cernicharo et al. in IRC +10216
via observations using the IRAM 30-m telescope.
The anion has also been observed in the low-mass star-forming region L1527 by
Sakai et al. and by
Agúndez et al. High resolution rotational
spectra of C4H- were issued by
McCarthy & Thaddeus and by
Like the first anion that was detected, C6H-,
C4H- is a linear
polyyne species. The anions of C2nH
species are stable because their
are quite substantial. The measured electron affinity of C4H reported by
Zhou et al. is 3.53 eV, which is comparable to the electron affinities of
like F (3.40 eV) and Cl (3.61 eV).