Abstract. Cyclic molecules of the general series c-C_nH₂ (n odd), where three of the carbon atoms form a triangle, have been supposed to be important species in cool cosmic objects. Here, we investigate the particular case of n = 7, i.e. c-C₇H₂, with the aim to obtain information about the rotational transitions by which the molecule could be identified in cool interstellar environments. Since this molecular species, to our knowledge, has not yet been fully studied experimentally we obtained the necessary structural parameters using a density functional theoretical approach employing the gradient corrected exchange-correlation functional B3LYP in conjunction with the extended cc-pVTZ basis set. The electronic structure calculations showed that c-C₇H₂ has at least nine stable isomers, the two lowest of which being energetically equal. The first one has C2v and the other Cs symmetry. Of these two structures we suggest the symmetric one for a search in cool cosmic objects. At the chosen level of electronic structure theory we obtained the rotational constants A = 7852.8326 MHz, B = 1565.0617 MHz, C = 1304.9804 MHz, and the electric dipole moment $\mu$ = 3.853 D. Though distortional effects might be significant they would not have a great influence on the qualitative behaviour of our investigation. We conclude that this molecule could be identified in cool interstellar environments by some of its rotational transitions 4₂₃ - 5₁₄, 3₂₂ - 4₁₃, 1₁₁ - 2₀₂, and 3₂₁ - 4₁₄ at 3.0, 6.5, 0.5, and 9.1 GHz, respectively, in absorption against the CMB.