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

Two Q branches of C2H2 near 716.3 and 719.9 cm(-1) belonging to the (v(4) + v(5))(0) - v(4)(1f) and 2v(5)(0) - v(5)(1f) bands, of Sigma <-- Pi symmetry, have been studied for He and N-2 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 C2H2-He are higher and narrower than those obtained for C2H2-N-2 at the same pressure as the result of smaller broadening coefficients and larger line-mixing effects in the former system, (C) 2000 Academic Press.