Hydrogen- and Helium-Broadening of Phosphine Lines

Pressure broadening of phosphine lines by hydrogen and helium at room temperature has been experimentally investigated by high-resolution Fourier transform spectroscopy. In the spectral region near 4-5 μm corresponding to the planetary observational window, about 900 lines were measured, mainly in the three weak transitions ν2 + ν4, 2ν2, and 2ν4. The retrieval of the linewidths and line intensities (along with the position of the baseline) was carried out by means of a nonlinear least-squares fit method. In both hydrogen- and helium-broadened spectra, it was found that for a given value of J the linewidths γ are nearly K-independent except for K values approaching J, for which a noticeable decrease of γ is observed. Within limits of experimental errors, the variation of γ with J may quite reasonably be considered as linear. For both perturbers. average broadening parameters γ(J) were proposed to be used for modeling purposes. Finally, the relative broadening ability of H2 as compared to He was determined and its average value found to be 1.85 ± 0.15.