FORMATION OF O(D-1) ATOMS IN THERMAL-DECOMPOSITION OF CO2

The formation of electronically excited oxygen atoms O(D-1) upon the t hermal decomposition of carbon dioxide is experimentally studied in a high-vacuum shock tube by atomic resonance absorption spectroscopy (AR AS) at 4102-6375 K and 20-190 kPa in the mixtures containing 100-1000 ppm CO2 in Ar. The rate constant of the increase in the concentration of O(D-1) atoms is found to be two or three orders of magnitude lower than the rate constant of the formation of oxygen in the ground state O(P-3). Comparison of the data obtained with the results of the direct measurements of the rate of CO2 decomposition and with the numerical calculations shows that the spin-forbidden reaction CO2((1) Sigma) + A r --> CO((1) Sigma) + O(P-3) + Ar, is the main channel of the thermal dissociation of carbon dioxide, whereas the contribution of the spin-a llowed reaction CO2((1) Sigma) + AR --> CO((1) Sigma) + O(D-1) + Ar un der the conditions studied does not exceed 10%. It is also shown that the thermodynamic equilibrium between the populations of O(P-3) and O( D-1) atoms is established even at the earliest stages of the decomposi tion.