Precision frequency comb spectroscopy of the 14N2O, 14N15NO, 15N14NO, and 15N2O isotopocules in the 3300 – 3550 cm–1 range

• High-resolution absorption coefficients, line positions and relative intensities of four N 2 O isotopocules measured using frequency comb Fourier transform spectroscopy in the 3300 – 3550 cm –1 range. • Sample obtained via chemical reduction of 15 N and 14 N-labelled nitrite. • Good agreement with HITRAN for 14 N 2 O, 14 N 15 NO, and 15 N 14 NO line positions and relative intensities. • Large discrepancies found for 15 N 2 O line positions in GEISA, IAO, and Ames-1 databases. • PGOPHER spectroscopic model for the ν 1 + ν 3 band of 15 N 2 O based on 80 assigned transitions. Nitrous oxide is a long-lived greenhouse gas. Its isotopic composition provides valuable insights into sources and sinks, and about the mechanisms of formation. A major challenge in the spectroscopic analysis of the isotopocule compositions is the availability of accurate spectroscopic parameters, particularly for the minor 15 N isotopocules. In this work, we introduce high-resolution spectroscopic measurements of four isotopocules of nitrous oxide: 14 N 2 O, 14 N 15 NO, 15 N 14 NO, and 15 N 2 O in the mid-infrared range of 3300 – 3550 cm –1 using a frequency comb-based Fourier transform spectrometer. The nitrous oxide samples were obtained from a chemical synthesis involving acid-catalyzed amine-borane reduction of equimolar amounts of 15 N isotopically enriched sodium nitrite and 14 N sodium nitrite. The high-resolution spectra, measured in a temperature-controlled single-pass absorption cell, were used to retrieve line center frequencies and relative intensities for a total of 426 rovibrational transitions of the ν 1 + ν 3 band of the four isotopocules, and of the one order of magnitude weaker 2ν 2 + ν 3 and ν 1 + ν 2 + ν 3 – ν 2 bands in the same spectral region. We compare the determined line center frequencies and relative intensities with spectroscopic parameters available in high-resolution molecular databases. For 14 N 2 O, 14 N 15 NO and 15 N 14 NO we find good agreement with the HITRAN database. The 15 N 2 O isotopocule is missing in HITRAN, and we find that its line center frequencies in the GEISA database, the Institute of Atmospheric Optics database, as well as the Ames-1 line list deviate severely from the comb measurements.