Atomic resonance absorption spectroscopy measurements on high-temperature CO dissociation kinetics

Abstract

The dissociation rate coefficient of CO was measured behind reflected shock waves in the temperature range 5500 < J<9000 K. By the use of the atomic resonance absorption spectroscopy (ARAS), the time-dependent formation of C and O atoms could be directly observed in the postshock reaction zone. The experiments were performed in mixtures of CO highly diluted in argon at pressures between 0.5 and 1.3 bar. The initial CO concentrations varied from 100 to 10,000 ppm. Assuming vibrational equilibrium, the data for the thermal decomposition of CO, (CO + Ar ^ C + O + Ar), can be represented by the following modified Arrhenius expression: k = 4.3 X1027 J-3-1 exp(-129,000 K/J) cn^mol-^-1 ±50%. Computer simulations based on a two-temperature model were not able to explain observed reaction induction times. Vibrational relaxation alone seems to have a negligible influence under the present conditions. The effect of impurities was minimized by keeping background pressure in the shock tube below 5xlO~ 7 mbar.