oai:edpsciences.org:dkey/10.1051/0004-6361:20040161

# Suggestions for an interstellar C

## Abstract

Laboratory detection of four isomers of C5H2 molecule have been reported by Travers et al. ([CITE]), McCarthy et al. ([CITE]), and Gottlieb et al. ([CITE]). They suggested for detection of the ring-chain isomer of C5H2 (c-C5H2) in cosmic objects, as it is the most stable one in comparison to the others. Two transitions $3_{1 3} {-} 2_{1 2}$ and $3_{0 3} {-} 2_{0 2}$ at 19.147 GHz and 19.606 GHz, respectively, of c-C5H2 have been detected in TMC-1. We suggest that the c-C5H2 may be identified in cool cosmic objects through its transition $3_{1 3} {-} 4_{0 4}$ at 4.3 GHz in absorption against the cosmic microwave background. Since in absence of availability of the collisional rates, we have used scaled values for them, we have checked the sensitivity of the lines on the rates by enhancing the rate for the transitions with $\Delta k_a = 0$ by a factor of 10. Though the transitions are not found sensitive, our results may be treated as qualitative in nature. This absorption line may play an important role for identification of c-C5H2 in cosmic objects