Line Positions and Intensities in the 2ν2/ν4 Vibrational System of 14NH3 near 5–7 μm

Abstract

Line positions and intensities belonging to the vibrational system 2ν2/ν4 of ammonia 14NH3 are measured and analyzed between 1200 and 2200 cm−1 in order to improve the molecular database. For this, laboratory spectra are obtained at 0.006 and 0.011 cm−1 unapodized resolution and with 4% precisions for the intensities using Fourier transform spectrometers located at the Kitt Peak National Observatory and the Jet Propulsion Laboratory. The observed data contain transitions of the ν4 fundamental band near 1626.276(1) and 1627.375(2) cm−1 (for s and a inversion upper states, respectively) and the 2ν2 overtone band near 1597.470(3) and 1882.179(5) cm−1 (for s and a inversion states, respectively). A total of 2345 lines with J′ ≤ 15 is assigned from which 2114 line positions with J′ ≤ 15 are fitted using an effective rotation–inversion–rotation Hamiltonian to achieve an rms of 0.003 cm−1 with 57 molecular parameters. Over 1200 intensity measurements are modeled to ±4.7% using 16 terms of the dipole moment expansion. A dyad model is used in order to model all the interactions expected within the 2ν2/ν4 system. The bandstrengths of 2ν2 (s ← a), 2ν2 (a ← s), and ν4 (s ← s and a ← a) are estimated to be 6.68(24), 0.201(5), and 116(3) cm−2 atm−1, respectively, at 296 K. The prediction generated by this study is available for planetary studies.