High-resolution rovibrational spectroscopy of c-C3H2+: The ν7 C–H antisymmetric stretching band

The ν7 antisymmetric C–H stretching fundamental of c-C3H2+ has been characterized in a cryogenic 22-pole ion trap by a novel type of action spectroscopy, in which the rovibrational excitation of c-C3H2+ is detected as a slowing down of the low-temperature reaction c-C3H2+ + H2 → C3H3++ H. Ninety-one rovibrational transitions with partly resolved fine structure doublets were measured in high resolution. Supported by high-level quantum chemical calculations, spectroscopic parameters were determined by fitting the observed lines with an effective Hamiltonian for an asymmetric rotor in a doublet electronic ground state, X˜ A12, yielding a band origin at 3113.6400(3) cm−1. Based on these spectroscopic parameters, the rotational spectrum of this astronomically important molecule is predicted