Rotationally Resolved Spectrum of the Degenerate Antisymmetric C–H Stretching Band of c-C3H3+

The rotationally resolved spectrum of the degenerate ν₄ antisymmetric C–H stretching band of the cyclopropenyl cation, c-C₃H₃⁺, the smallest aromatic hydrocarbon cation, has been recorded employing leak-out-spectroscopy (LOS) in a cryogenic 22-pole ion trap instrument operated at T = 42 K. About 370 lines were measured in the region 3110–3150 cm^–1 and assigned to rovibrational transitions of the fundamental antisymmetric C–H stretching band. Spectroscopic parameters have been refined compared to the previous experimental work from the group of Harold Linnartz [Zhao et al., Astrophys. J. Lett. 2014, 791, L28] and previous high-level theoretical predictions [Huang et al., J. Phys. Chem. A 2011, 115, 5005–5016]. Details of the spectral signatures allow for a thorough comparison of action spectroscopy in low-temperature ion traps to cavity ring down spectroscopy in a free-jet cooled discharge.