SIMBAD references

Laboratory detection of four isomers of C₅H₂ molecule have been reported by Travers et al. (1997ApJ...483L.135T), McCarthy et al. (1997Sci...275..518M), and Gottlieb et al. (1998ApJ...509L.141G). 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 19.147GHz and 19.606GHz, 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 4.3GHz 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 Δk_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.