Temperature-dependent line mixing in the R-branch of the v3 band of methane.

• CH 4 -N 2 line mixing parameters empirically-determined for R branch transitions J ″ = 4--18. • High spectral resolution study of the R (15) manifold for sensing in combustion. • Thermodynamic scaling of collisional effects examined up to 1600 K and 25 atm. High-temperature line mixing behavior was studied for 15 R-branch line manifolds in the v 3 band of methane from 3.14 µm to 3.28 µm. The temperature-dependence of the line mixing parameters for the R (4) to R (18) manifolds perturbed by nitrogen were empirically-determined over a range of temperatures from 300–1000 K using Fourier transform infrared spectroscopy in a heated gas cell. A more extensive line mixing investigation of the rovibrational transitions comprising the R (15) manifold was performed at lower pressures (0.3–2 atm) using laser absorption spectroscopy from 300–1600 K in both the heated cell and a high-enthalpy shock tube. Measured spectra were modeled and fit using both a modified exponential gap model and a perturbation theory-based first-order model to capture the pressure- and temperature-dependence of the line mixing effects. The modified exponential gap model was found to sufficiently capture the line mixing behavior at pressures greater than 20 atm, while perturbation theory enables more accurate characterization of the behavior at the lower pressures. The applicability of both the modified exponential gap model and perturbation theory is also discussed with analyses of the fitting residuals and the parameter uncertainties to provide reference for the use of the two empirical models in simulating the R-branch of the v 3 band of 12CH 4 over a wide range of thermodynamic conditions. [ABSTRACT FROM AUTHOR]