Estimation of line parameters under line mixing effects: the nu(3) band ofCH4 in helium

Spectra of CH4-He mixtures were measured in the P and R branch regions of n u (3) vibration-rotation band at lower pressures of 0.26-1.0 bar and for th e whole band at higher pressures up to 90 bar. The line broadening coeffici ents were found from lower pressure data for the lines of the P branch. The se coefficients were calculated in the framework of the Robert and Bonamy s emi-classical approach. In general, they agree with the experimental ones, but a small J-dependent deviation was observed. Line mixing effects were ob served at all pressures. At higher pressures they were interpreted in terms of the adjusted branch-coupling model. At lower pressures line mixing effe cts were found to be especially pronounced in the region of the relatively weak lines forming the clusters from R(16) to R(19). (C) 2001 Published by Elsevier Science Ltd.