Abstract
A theoretical model based on the energy corrected sudden (ECS) approximation is used to account for line-mixing effects in infraredQbranches of parallel bands of CO2. Measurements have been made using a tunable difference frequency spectrometer system in a Π–Π transition: spectra of the 1111II← 0110IQbranch near 3580.3 cm−1have been recorded at room temperature for CO2–He and CO2–N2mixtures in the 0.1–1 atm total pressure range. Comparisons of experimental and computed spectra prove the quality of the ECS approach. It is shown that the influence of line mixing on the shape of parallelQbranches is very weak and much smaller than in perpendicular transitions. This result is analyzed in detail and explained in terms of the effects of the vibrational angular momenta on the dipole transition moments and vector coupling coefficients involved in the relaxation operator elements. The effects of collisions of CO2with N2and He are compared and discussed.
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