KINETICS OF CO2 DISSOCIATION AT MULTIMODAL VIBRATIONAL NONEQUILIBRIUM

Our main concern here is to establish a correlation between the dissoc iation rate and vibrational energy distribution of CO2 molecules. The experimental approach consisted in setting up multimodal vibrational n onequilibrium in shock-heated CO2/N-2/Ar mixtures and measuring the ra te of CO2 decomposition by means of high-precision time-resolved atomi c resonance absorption spectroscopy (ARAS) of oxygen atoms formed earl y in the vibrational relaxation. Measurements were taken in mixtures c ontaining 2000 ppm CO2 and N-2 and in 10%N-2+Ar at temperatures 2326-2 855 K and pressures 0.75-2.59 atm. A tentative analysis of the obtaine d data has led us to conclude that the rate of CO2 decomposition can b e qualitatively described in terms of a macroscopic rate constant for dissociation dependent on the vibrational temperature T-3 of low-lying levels of the antisymmetric mode. For the purpose of quantitative des cription of CO2 dissociation at vibrational nonequilibrium we develope d a numerical model combining an exact approach taking into account vi brational levels of reacting molecules with the ''ladder'' approximati on of this molecule. The underlying principle of this model allowing f or intramodal and intermodal energy exchange and dissociation is that relaxation of low-lying vibrational levels of CO2 should be modelled w ith a pinpoint accuracy, while higher-excited states of all the modes should be described within the ''ladder'' approximation. A kinetic dis sociation mechanism involving interaction of highly excited states of CO3 and N-2 is proposed, and the rate constants for the included energ y exchange processes are evaluated.