Research Note

Suggestions for an interstellar C₅H₂ search^*

School of Physical Sciences, SRTM University, Nanded 431 606, India e-mail: sch@iucaa.ernet.in

Received: 21 May 2003
Accepted: 5 May 2004

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 and 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 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 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.