Line mixing effects in the 1 ← 0 and 2 ← 0 CO bands perturbed by CO and N 2 from low to high densities

Abstract

The shapes of the fundamental and first overtone bands of compressed CO or CO compressed by N 2 at densities up to 455 Amagat and various temperatures have been analyzed. Important deviations from an additive superposition of Lorentzian lines have been explained by collision-induced line mixing effects calculated within the impact approximation. By taking into account properly the angular momentum coupling in spectroscopic relaxation cross sections and using the energy corrected sudden (ECS) model, we have obtained quite satisfactory agreement with bandshapes at moderate densities in the center as well as the near wing region. The deviations from the Lorentz absorption in the microwindows between CO lines at low density can be correctly predicted theoretically but only at room and high temperatures. The discrepancy arising at high density between experimental and calculated spectra is mainly attributed to the non-validity of the impact and binary collision approximations, the finite volume of the molecule, and imperfections in the calculated relaxation matrix.