Suggestions for an interstellar C7H2 search

Laboratory detection of the ring-chain molecule C-C7H2 has been reported by McCarthy et al. [McCarthy, M.C., Travers, M.J., Gottlieb, C.A., Thaddeus, P., 1997. A&A 483, L139]. Two ring-chain molecules c-C3H2 and C-C5H2 of this series have already been detected in the cosmic objects. We suggest that the C-C7H2 may be identified in cool cosmic objects through its transitions 4(14)-5(05), 5(15)-6(06), 6(16)-7(07) and 7(17)-8(08) at 23.241, 21.105, 18.953 and 16.787 GHz, respectively, in absorption against the CMB. Since, in absence of the availability of collisional rates, we have used scaled values for them, we have checked the sensitivity of the results on the collisional rates, by enhancing the rates for the transitions with Delta k(a) = 0 by a factor of 10. Though the transitions are not found sensitive to the collisional rates, our results still may be treated as qualitative in nature. These absorption lines may play an important role for identification of c-C7H2 in cool cosmic objects. (C) 2005 Elsevier B.V. All rights reserved.