Estimation of line parameters under line mixing effects - The nu3 band of CH4 in helium

Spectra of CH4-He mixtures were measured in the P and R branch regions of nu3 vibration-rotation band at lower pressures of 0.26-.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 semiclassical 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). (Author)