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${}^{-1}$ 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 ${}^{14}$NH${}_3$ lines were measured in the 5650–6350 cm${}^{-1}$ 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${}^{-1}$ range. Accurate jet spectra calibration was achieved using CH${}_4$ reference line positions known with kHz accuracy. The position agreement with the FTS data is within the $4\times {10}^{-4}$ cm${}^{-1}$ uncertainty of the positions measured in the jet expansion. A recommended line list of 5620 transitions is provided for ${}^{14}$NH${}_3$ in the considered 5650–6350 cm${}^{-1}$ region.

GRAPHICAL ABSTRACT

Keywords:

• Ammonia
• absorption spectroscopy
• near infrared
• rovibrational assignment

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

This research was supported by the joint Slovak-Czech-French Danube Region project (DS-FR-19-0050), and by the Slovak Research and Development Agency (contract number APVV-19-0386). This work was also a contribution to the CPER research project CLIMIBIO. The authors thank the French Ministère de l'Enseignement Supérieur et de la Recherche, the Hauts de France Region and the European Funds for Regional Economic Development for their financial support to this project. This work was performed in the frame of the ANR project e_PYTHEAS (ANR-16-CE31-005).