Line mixing effects on the shapes of fluoroform IR absorption bands perturbed by foreign gases

The IR absorption spectra of CHF3 in mixtures with He, Ar and N-2 were recorded in the region of 400-800 cm(-1) using the Bruker IFS-28 Fourier transform spectrometer at resolution of 0.6 cm(-1). The shapes of the parallel nu(3)(A(1)) and perpendicular nu(6)(E) bands were studied at perturbing gas pressure range of 25-100 atm. The observed behavior of the shapes for these two bands at the pressure increase is similar. The Q-branch widths increase at the pressure rise for all pertubers, but the slopes are quite different from those for individual lines. The Q-branch broadening for He mixture is much smaller than that for Ar mixture (for individual lines these values are close). To the contrary, the Q-branch broadening for Ar and N2 mixtures is similar whereas for the lines these values are different. The Hermann-Wallis factor was introduced to describe the line intensity distribution in P and R branches. The shape calculations were performed in the approximation of Lorentzian lines sum. At higher pressures the calculated shapes are totally different from the experimental ones. We attributed this difference to line mixing effect. We used the adjusted branch coupling model in shape calculations to estimate this effect on the observed shapes. The results of the calculations explain qualitatively the observed band shape transformations.