The absorption spectrum of nitrous oxide between 8325 and 8622 cm−1

Highlights: • High sensitivity CRDS of the weak absorption spectrum of N₂O between the 8325-8622 cm⁻¹. • More than 3300 lines of 47 bands of ¹⁴N₂¹⁶O, ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O, and ¹⁴N₂¹⁸O are measured. • Only five bands were previously reported in the region, with no intensity information. • Bands corresponding to a ΔP= 15 variation of the polyad number are reported for the first time. • In the considered region, the HITRAN and HITEMP databases show deficiencies in terms of completeness and accuracy. The weak high-resolution absorption spectrum of natural nitrous oxide has been recorded by high sensitivity cavity ring down spectroscopy (CRDS) near 1.18 µm. The frequency scale of the spectra was obtained by coupling the CRDS spectrometer to a self-referenced frequency comb. The room temperature recordings, performed with a pressure of 1 Torr, cover the 8325-8622 cm⁻¹ spectral interval where previous observations were very scarce. More than 3300 lines belonging to four N₂O isotopologues (¹⁴N₂¹⁶O, ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O, and ¹⁴N₂¹⁸O) are measured with a position accuracy better than 1 × 10⁻³ cm⁻¹ for most of the lines. Line intensities at room temperature range between 1.2 × 10⁻²⁵ and 3.8 × 10⁻³⁰ cm/molecule. The rovibrational assignments were obtained by comparison with predictions based on the global modeling of the line positions and intensities performed within the framework of the method of effective operators. The band-by-band analysis led to the determination of the rovibrational parameters of a total of 47 bands. All identified bands belong to the ΔP= 14-16 series of transitions, where P=2V₁+V₂+4V₃ is the polyad number (V_{i= 1-3} are the vibrational quantum numbers). Among these bands, only five were previously observed and bands of the ΔP= 15 series are reported for the first time. Local resonance perturbations affecting two bands are identified and analyzed. The position and intensity comparisons to the HITRAN2016 and HITEMP2019 spectroscopic databases are discussed. The HITRAN line list is limited to only four (calculated) bands of the ¹⁴N₂¹⁸O isotopologue in the studied region while ΔP= 15 bands are missing in the HITEMP list. The present work will help to improve future versions of the spectroscopic databases of nitrous oxide, a strong greenhouse gas.