Determination of vibrational CO2 distributions in thermodynamically-nonequilibrated rarefied flows by use of radiational characteristics in the 15 μm band

A method for determination of the vibrational distributions and populations of individual vibrational levels of vibrationally-nonequilibrated carbon dioxide in bend-stretch manifold and asymmetric stretching mode was developed and substantiated. The method is based on the measurements of integrated radiation intensity in the wide spectral intervals of the 15 μm CO₂ band and total emissivities of its appropriate Q-branches. Computations of radiation intensities and emissivities in P and R-branches were performed by using vibrational-rotational band models and in Q-branches by the direct “line-by-line” integration.It was shown that vibrational temperature of CO₂ asymmetric stretching mode may be determined from the measurements of integrated radiation intensity of the 15 μm band. The populations of individual levels of the bend-stretch manifold may be obtained from the measurements of total emissivities of some Q-branches of the 15 μm band.The procedure of the CO₂ lower vibrational levels populations determination under the conditions typical of 18 μm and 9–11 μm CO₂ laser cavities is described.