Far-infrared 14NH3 line positions and intensities measured with a FT-IR and AILES beamline, Synchrotron SOLEIL

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Extensive measurements of line positions and intensities are reported for the inversion-rotation and rovibrational transitions of 14NH3 in the 50–660cm−1 region. This study analyzes high-resolution (0.00167cm−1, unapodized) Fourier-transform spectra of high purity (99.5%) normal ammonia sample obtained using the AILES beamline of Synchrotron SOLEIL. The experimental conditions are designed to study transitions with intensities weaker than 1×10−22cm−1/(moleculecm−2) at room temperature. Line positions and intensities of more than 2830 transitions of 14NH3 are measured and compiled after proper quality control; the features from minor isotopologues (15NH3 and NH2D) and H2O are identified and excluded. Based on the predictions of recent work from the empirical Hamiltonian modeling, systematic quantum assignments are made for 2047 transitions from eight bands including four inversion-rotation (gs, v2, 2v2, and v4) and four ro-vibrational bands (v2–gs, 2v2–v2, v4–v2, and 2v2–v4), as well as covering their ΔK=3 forbidden transitions. The measured line positions for the assigned transitions are in an excellent agreement (typically better than 0.001cm−1) with the predictions in a wide range of J and K for all the eight bands. The comparison with the HITRAN 2012 database is also satisfactory, although systematic offsets are seen for transitions with high J and K and those from weak bands. Also we note that out of the eight bands, the 2v2–v4 has not been listed in the HITRAN 2012 database. Differences of 20% are seen between our measured and calculated intensities depending on the bands. For line positions, greater differences are found for some NH3 bands in HITRAN 2012 than recent predictions. Measurements of the individual line positions and intensities are presented for the eight bands, and the final spectroscopic line positions and intensities are compiled as an electronic supplement.