The ammonia absorption spectrum revisited between 5650 and 6350 cm−1

Abstract

The ammonia spectrum is revisited in the important 1.6 µm atmospheric transparency window between 5650 and 6350 cm on the basis of recently recorded high-resolution Fourier transform spectra. These spectra offer an improved frequency sampling and better traceability of the measurement conditions compared to previously studied Kitt Peak spectra (Cacciani et al. J. Quant Spectrosc Radiat Transf 2021; 258:107334. https://doi.org/10.1016/j.jqsrt.2020.107334). Overall, 4812 NH lines were measured in the 5650–6350 cm region corresponding to 4866 transitions including 2066 new ones compared with our previous study, included in the HITRAN2020 database. The energy of 1023 upper state levels (including 107 new ones) was derived from 2608 assigned transitions. Independently, ammonia spectra recorded in a supersonic jet expansion using a tunable extended cavity diode laser allow us to check the absolute transition energies in the 5980–6080 cm range. Accurate jet spectra calibration was achieved using CH reference line positions known with kHz accuracy. The position agreement with the FTS data is within the  cm uncertainty of the positions measured in the jet expansion. A recommended line list of 5620 transitions is provided for NH in the considered 5650–6350 cm region.