Carbon Dioxide Thermal Decomposition: Observation of Incubation

Abstract

Abstract Incubation prior to the thermal decomposition of CO2 is observed for the first time behind shock waves, confirming the expected bottleneck in collisional activation of this triatomic molecule. The thermal decomposition of carbon dioxide has been investigated behind reflected shock waves at temperatures of 3200–4600 K and pressures of 45–100 kPa. Ultraviolet laser absorption was used to monitor the CO2 concentration with microsecond time resolution, allowing observation of a pronounced incubation period prior to steady CO2 dissociation. Master equation simulations, with a simple model for collisional energy transfer, were carried out to describe the measured incubation times and dissociation rate coefficient. The second order rate coefficient for CO2 dissociation was found to be 3.14 × 1014 exp(−51300 K/T) cm3 mol−1 s−1. The number of incubation collisions was found to range from 7 × 103 at 4600 K to 3.5 × 104 at 3200 K. The master equation simulations suggest that the energy transferred per collision must have a greater than linear dependence on energy.