High-resolution investigation of the spin-rotation doublets of 14NO2 at 6.2 μm mid-infrared region using cavity ring-down spectroscopy

Nitrogen dioxide ((NO2)-N-14) exhibits a unique doublet structure due to the presence of its unpaired electron, which results in a nonzero electronic angular momentum in the ground electronic state of the molecule. In this study, an investigation into high-resolution rovibrational spectral features associated with the spin-rotation doublets of (NO2)-N-14 was conducted using an external-cavity quantum cascade laser (EC-QCL)-coupled cavity ring-down spectrometer operating at 6.2 mu m. Four spin-split doublets belonging to the (R) R branch of the (0 0 1)-(0 0 0) fundamental band were probed in the mid-IR spectral region. The air broadening and self-broadening coefficients were reported explicitly for each doublet component for the first time, to the best of our knowledge. The line-intensities were also quantified, and they were compared to the HITRAN database, revealing good agreement (<4% discrepancy).