An Observational Investigation of the Identity of B11244 (l-C_3H^+/C_3H^–)

Abstract

Pety et al. have reported the detection of eight transitions of a closed-shell, linear molecule (B11244) in observations toward the Horsehead photodissociation region (PDR), which they attribute to the l-C_3H^+ cation. Recent high-level ab initio calculations have called this assignment into question; the anionic C_3H^– 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_3H^+ and C_3H^–. We find no observational evidence of K_a = 1 lines, which should be present were the carrier indeed C_3H^–. Additionally, we find a strong anticorrelation between the presence of known molecular anions and B11244 in these regions. Finally, we discuss the formation and destruction chemistry of C_3H^– in the context of the physical conditions in the regions. Based on these results, we conclude there is little evidence to support the claim that the carrier is C_3H^–.

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