Line shape narrowing in carbon dioxide at high pressures

Abstract

The description of the narrowing effect at high pressures is demonstrated on the example of CO2-He absorption for Q-, P-, and R-branches and for the head of the R-branch. The problem is focused on the physical meaning of this phenomenon that should be associated with the angular and translation momentum transfer to matter from the photon absorbed. The effect is described in the approximation of the single line without the conventional line mixing. A narrowing function is introduced that links the absorption in the resonance region with the one in far wings. This function enlarges the absorption of a single line approximately in two times in the resonance region at high pressures and decreases the one approximately in 20 times in far wings in comparison with the Lorentzian, independently of the type of molecule and pressures. The halfwidth of a single line is assumed to have a nonlinear pressure dependence and approaches to a saturated value at high pressures.