Line shape parameters of PH₃ transitions in the Pentad near 4–5 μm: Self-broadened widths, shifts, line mixing and speed dependence

Journal Article · Fri Aug 01 00:00:00 EDT 2014 · Journal of Molecular Spectroscopy, 302:17-33

DOI:https://doi.org/10.1016/j.jms.2014.06.003· OSTI ID:1170472

Malathy Devi, V.; Benner, D. C.; Kleiner, Isabelle; Sams, Robert L.; Fletcher, Leigh N.

Accurate knowledge of spectroscopic line parameters of PH₃ is important for remote sensing of the outer planets, especially Jupiter and Saturn. In a recent study, line positions and intensities for the Pentad bands of PH₃ have been reported from analysis of high-resolution, high signal-to noise room-temperature spectra recorded with two Fourier transform spectrometers (2014) [1]. The results presented in this study were obtained during the analysis of positions and intensities, but here we focus on the measurements of spectral line shapes (e.g. widths, shifts, line mixing) for the 2ν₄, ν₂ + ν₄, ν₁ and ν₃ bands. A multispectrum nonlinear least squares curve fitting technique employing a non-Voigt line shape to include line mixing and speed dependence of the Lorentz width was employed to fit the spectra simultaneously. The least squares fittings were performed on five room-temperature spectra recorded at various PH₃ pressures (~2–50 Torr) with the Bruker IFS-125HR Fourier transform spectrometer (FTS) located at the Pacific Northwest National Laboratory (PNNL), in Richland, Washington. Over 840 Lorentz self-broadened half-width coefficients, 620 self-shift coefficients and 185 speed dependence parameters were measured. Line mixing was detected for transitions in the 2ν₄, ν₁ and ν₃ bands, and their values were quantified for 10 A+A- pairs of transitions via off-diagonal relaxation matrix element formalism. The dependences of the measured half-width coefficients on the J and K rotational quanta of the transitions are discussed. The self-width coefficients for the ν₁ and ν₃ bands from this study are compared to the self-width coefficients for transitions with the same rotational quanta (J, K) reported for the Dyad (ν₂ and ν₄) bands. The measurements from present study should be useful for the development of a reliable theoretical modeling of pressure-broadened widths, shifts and line mixing in symmetric top molecules with C_3v symmetry in general, and of PH₃ in particular.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1170472
• Report Number(s): PNNL-SA-105193
• Journal Information: Journal of Molecular Spectroscopy, 302:17-33, Journal Name: Journal of Molecular Spectroscopy, 302:17-33
• Country of Publication: United States
• Language: English