Line-mixing effects in He- and N₂-broadened Σ↔Π infrared Q branches of N₂O

Two Q branches of N₂O near 579.3 and 2798cm^-1 belonging to the 2ν₂ ^0e-ν₂ ^1f and ν₂+ν₃ bands, respectively, of Σ←Π and Π←Σ symmetry, have been studied for He and N₂ perturbers at pressures ranging from 0.1 to 2 atm, using a tunable diode laser and a difference-frequency laser spectrometer. To interpret the line-mixing effects in these spectra, we have applied a model based on the energy corrected sudden approximation whose parameters have been only derived from line-broadening data for N₂O-He and also from the measured absorption by the Q branches for N₂O-N₂. This model provides a satisfactory agreement with experimental band shapes, whatever the band, the perturber and the pressure considered. Significantly larger line-mixing effects are shown for N₂O-He with respect to N₂O-N₂. Finally, the assumption made in the calculations to treat separately the couplings in the even and odd j levels appears to have a negligible influence on the resulting band shapes.