An observational investigation of the identity of B11244 ($l$-C${}_3$H${}^{+}$/C${}_3$H${}^{-}$)

Abstract

Pety et al. (2012) have reported the detection of eight transitions of a closed-shell, linear molecule (B11244) in observations toward the Horsehead PDR, which they attribute to the $l$-C${}_3$H${}^{+}$ cation. Recent high-level \textit{ab initio} calculations have called this assignment into question; the anionic C${}_3$H${}^{-}$ molecule has been suggested as a more likely candidate. Here, we examine observations of the Horsehead PDR, Sgr B2(N), TMC-1, and IRC+10216 in the context of both $l$-C${}_3$H${}^{+}$ and C${}_3$H${}^{-}$. We find no observational evidence of $K_a=1$ lines which should be present were the carrier indeed C${}_3$H${}^{-}$. Additionally, we find a strong anti-correlation between the presence of known molecular anions and B11244 in these regions. Finally, we discuss the formation and destruction chemistry of C${}_3$H${}^{-}$ in the context of the physical conditions in the regions. Based on these results, we conclude there is little evidence to support the carrier is C${}_3$H${}^{-}$.

17 pages, 3 figures, accepted in the Astrophysical Journal

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