June 2011

Butadiynyl radical anion

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 Amano.

Like the first anion that was detected, C6H-, C4H- is a linear polyyne species. The anions of C2nH species are stable because their electron affinities 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 halogens like F (3.40 eV) and Cl (3.61 eV).

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