Estimation of line parameters under line mixing effects: the ν3 band of CH 4 in helium

Abstract

Spectra of CH 4–He mixtures were measured in the P and R branch regions of ν 3 vibration–rotation band at lower pressures of 0.26–1.0 bar and for the whole band at higher pressures up to 90 bar. The line broadening coefficients were found from lower pressure data for the lines of the P branch. These coefficients were calculated in the framework of the Robert and Bonamy semi-classical approach. In general, they agree with the experimental ones, but a small J-dependent deviation was observed. Line mixing effects were observed at all pressures. At higher pressures they were interpreted in terms of the adjusted branch-coupling model. At lower pressures line mixing effects were found to be especially pronounced in the region of the relatively weak lines forming the clusters from R(16) to R(19).