Line broadening and line mixing effect in ν3 band of CH4 perturbed by He gas

The spectra of CH4-He mixtures were measured in the P- and R-region of nu(3) vibration-rotation band at lower pressures of 0.2-1.0 bar and for the whole band at higher pressures up to 90 bar. The broadening line coefficients were found from lower pressure data for the lines of P branch. These coefficients were calculated in the frame of the semi-classical approach. They agree with the experimental values, but a small J-dependent deviation was observed. The line mixing effect was observed. At higher pressure it was interpreted in the terms of the adjusted branch-coupling model. At lower pressure the line mixing effect was found to be especially pronounced in the region of relatively weak lines forming the clusters R(16)-R(19).