Line positions and intensities of the phosphine (PH3) Pentad near 4.5μm

Abstract In order to improve the spectroscopic database for remote sensing of the giant planets, line positions and intensities are determined for the five bands (2ν 2 , ν 2  + ν 4 , 2ν 4 , ν 1 and ν 3 ) that comprise the Pentad of PH 3 between 1950 and 2450 cm −1 . Knowledge of PH 3 spectral line parameters in this region is important for the exploration of dynamics and chemistry on Saturn, (using existing Cassini/VIMS observations) and future near-IR data of Jupiter from Juno and ESA’s Jupiter Icy Moons Explorer (JUICE). For this study, spectra of pure PH 3 from two Fourier transform spectrometers were obtained: (a) five high-resolution (0.00223 cm −1 ), high signal-to-noise (∼1800) spectra recorded at room temperature (298.2 K) with the Bruker IFS 125HR Fourier transform spectrometer (FTS) at the Pacific Northwest National Laboratory (PNNL), Richland, Washington and (b) four high-resolution (at 0.0115 cm −1 resolution), high signal-to-noise (∼700) spectra recorded at room temperature in the region 1800–5200 cm −1 using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory (NSO) on Kitt Peak. Individual line parameters above 2150 cm −1 were retrieved by simultaneous multispectrum fittings of all five Bruker spectra, while retrievals with the four Kitt Peak spectra were done in the 1938–2168 cm −1 range spectrum by spectrum and averaged. In all, positions and intensities were obtained for more than 4400 lines. These included 53 A+A− split pairs of transitions (arising due to vibration–rotation interactions (Coriolis-type interaction) between the ν 3 and ν 1 fundamental bands) for K ″ = 3, 6, and 9. Over 3400 positions and 1750 intensities of these lines were ultimately identified as relatively unblended and modeled up to J  = 14 and K  = 12 with rms values of 0.00133 cm −1 and 7.7%, respectively. The PH 3 line parameters (observed positions and measured intensities with known quantum assignments) and Hamiltonian constants are reported. Comparisons with other recent studies are discussed.

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