Speed-dependent broadening and line mixing in CH4 perturbed by Ar and N-2 from multispectrum fits

Speed-dependent broadenings and shifts have been determined for the P and R branches of the nu(3) band of CH4 perturbed by Ar and N-2 using a multispe ctrum fitting analysis of high-resolution tunable difference-frequency lase r spectra recorded at pressures less than or equal to 67 kPa. For J greater than or equal to 3, the tetrahedral fine structure components in each J ma nifold are collisionally coupled and exhibit significant interference. The coupled lines are treated using a speed-dependent first-order line-mixing p rofile and are compared to a speed-independent full relaxation matrix inver sion procedure with off-diagonal coupling elements calculated from an atom- atom Lennard-Jones potential model, (C) 2000 Elsevier Science Ltd. All righ ts reserved.