Line-mixing effects in He- and N₂-broadened ∑← Π infrared Q branches of C₂H₂

Two Q branches of CH near 716.3 and 719.9 cm belonging to the (ν + ν) - ν/ and 2ν-ν bands, of 2 ∑ → Π symmetry, have been studied for He and N perturbers at pressures ranging from 0.05 to 1 atm, using a tunable diode-laser spectrometer. To interpret the line-mixing effects observed 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. This model provides satisfactory agreement with experimental bandshapes for both bands and perturbers, especially at pressures higher than 0.1 atm. The Q-branch profiles for CH-He are higher and narrower than those obtained for CH-N at the same pressure as the result of smaller broadening coefficients and larger line-mixing effects in the former system.