The structures of the cyclic-C3H radical — an interstellar molecule

The equilibrium structure of the cyclic C3H radical was obtained by ab initio computation. The total energy at a Cs optimum structure is lower than that of a C2v optimum structure by only 10−4 hartree and the adiabatic potential surface for the antisymmetric motion is so flat that no locally bound vibrational level exists around the Cs minimum; the force constant for the CC antisymmetric stretching mode is about one sixth of that for the CC symmetric stretching mode.