Highly accurate potential energy surface and dipole moment surface for nitrous oxide and 296K infrared line lists for ¹⁴N₂¹⁶O and minor isotopologues

Abstract

To facilitate the data analysis of current and future high-resolution space telescope missions, we adopt ‘Best Theory + Reliable High-resolution Experiment’ (BTRHE) strategy to develop highly accurate infrared line lists for nitrous oxide (N₂O). The ‘Ames-1’ potential energy surface (PES) is a CCSD(T)/aug-cc-pVQZ PES refined using selected HITRAN experimental data, with σ_rms = 0.02–0.03 cm^-1 for five isotopologues. The ‘Ames-1’ dipole moment surface (DMS) is fitted from CCSD(T)/aug-cc-pV(T,Q,5)Z dipoles extrapolated to one electron basis set limit. Using the Ames-1 PES and DMS, Ames-296K line lists are computed in the full range of 0–15,000 cm^-1 for 12 N₂O isotopologues, with S_296K ≥ 10⁻³¹ cm^-1/molecule.cm^-2. The reliability and consistency of Ames-296K intensity predictions (S_Ames) are demonstrated through comparisons with HITRAN (S_HITRAN), NOSL-296 (S_NOSL), recent observed intensities (S_obs) and Effective Dipole Model (EDM) intensities (S_EDM). Agreements and discrepancies are discussed, along with preliminary uncertainty estimate for S_Ames. The S_Ames provides a good constraint to prevent substantial errors in intensity predictions (e.g. for weak bands and minor isotopologues) and can be further improved. Ames-296K and NOSL-296 may complement each other to provide improved input for future database updates, combining the strengths of EH/EDM and BTRHE approaches. Data available at https://doi.org/10.5281/zenodo.7888194 and https://doi.org/10.48667/9kmk-0334.

GRAPHICAL ABSTRACT

KEYWORDS:

• Nitrous Oxide
• dipole moment surface
• rovibrational IR line list
• potential energy surface refinement
• IR intensity prediction

Acknowledgements

We gratefully acknowledge support from the NASA Grants 18-APRA18–0013 and 18-XRP18_2–0029. X.H. acknowledges the support by NASA/SETI Institute Co-operative Agreements 80NSSC19M0121 and 80NSSC20K1358. We thank Dr. Tashkun (IAO) and Dr. Campargue (Grenoble) for kindly sharing data and helpful discussions. We thank Dr. Gordon (Harvard CfA, HITRAN) for comments and discussions. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center.

Dr. Timothy J. Lee tragically passed away during this work. As a senior scientist fascinated with the significance of highly accurate molecular IR line lists in exoplanetary research, Tim served as the technical officer for our project, helping it running smoothly to study the function and role of biosignature molecules like N₂O in atmospheres. We devote this paper to this memorial issue honouring Tim's contribution and continuous passion.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by NASA ROSES grants: [Grant Numbers 18-APRA18-0013 and 18-XRP18_2-0029].