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 <i>T</i> = 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., <i>Astrophys. J. Lett.</i> 2014, 791, L28] and previous high-level theoretical predictions [Huang et al., <i>J. Phys. Chem. A</i> 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.