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Towards an Accurate Line List of NH₃ for Planetary Atmospheres

Presentation #402.02 in the session Extrasolar Planet Atmospheres — iPoster Session.

Published onJun 29, 2022
Towards an Accurate Line List of NH₃ for Planetary Atmospheres

HITRAN [1] is a leading molecular spectroscopic database that contains line-by-line parameters for many key molecules and isotopologues for the remote sensing of planetary atmospheres. Among these molecules, ammonia is an important species due to its prevalence terrestrially and in planetary atmospheres. Therefore a highly accurate line list is necessary for high-resolution applications such as cross correlation spectroscopy. Recently, a number of improvements to the ammonia line list was included for HITRAN2020 [1], however certain spectral regions (e.g., 3800-4800 cm-1) remain incomplete. In addition, a large proportion of lines that are provided in the database in these regions have limited spectral assignments, which makes it difficult to model spectra at temperatures higher or lower than that on Earth.

Work is underway to expand the spectral range and applicability of the ammonia line list in HITRAN for planetary atmospheres. For example, we recently compared a high-resolution experimental FTS spectrum of NH3 at room temperature [2] to spectra calculated using both ab initio and empirical line lists for the 3800-4800 cm-1 region. From these comparisons, we were able to assign numerous transitions using the ab initio work [3], which has reduced the RMSE in the calculated spectra by 17%. The recent improvements to the HITRAN line list for ammonia will be summarized and further steps toward an accurate line list for planetary applications will be presented.

This research is covered by NASA grant 80NSSC20K0962 and was partly carried out with student support from the National Science Foundation under Grant No. 1745460.

References: 1. Gordon, et al., 2022, JQSRT, 277, 107949. 2. Beale et al., 2017, JQSRT, 203: 410-416. 3. Coles et al., 2019, MNRAS, 490, 4638-4647.

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