Collisional Narrowing and Spectral Shift in CARS Spectra of Molecular Nitrogen and Oxygen at Pressures up to 2500 bar and Temperatures of 850 K

Vibrational-rotational CARS spectra of molecular nitrogen and oxygen at high densities and temperatures are recorded using a scanning CARS-spectrometer. Measurements are performed at pressures up to 2500 bar and temperatures up to 850 K. The spectral line position and halfwidth of the fully collapsed Q-branch are determined for pure N2, O2, N2/O2 Mixtures and Ar/O2 mixtures. Comparisons of the experimental data with different theoretical models for the rotational energy transfer are also presented. Three quantum mechanical approaches (MEG-, ECS-, PEG-laws) are compared with a classical description of the relaxation process treating the angular momentum as a continuous variable.