Line-Mixing Effects in He- and N2-Broadened Σ ← Π Infrared Q Branches of C2H2

Abstract

Two Q branches of C2H2 near 716.3 and 719.9 cm−1 belonging to the (ν4 + ν5)0 − ν1f4 and 2ν05–ν1f5 bands, of Σ ← Π symmetry, have been studied for He and N2 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–N2 at the same pressure as the result of smaller broadening coefficients and larger line-mixing effects in the former system.