Interferometric studies of carbon dioxide dissociation in a free-piston shock tube

Time-resolved interferometry is used to measure the dissociation rate of carbon dioxide in a free-piston shock tube. Over the temperature range of 2500–7000 K the dissociation rate is kd=7.5×1012 T1/2 exp[−(104 000±2500)/RT] cc/mole-s. This gives an activation energy of (104±2.5 kcal/mole+(1/2) RT) in agreement with recent theoretical predictions. The present data are also fitted to the RRK expression and gives a threshold energy of 132 kcal/mole. The effect of impurities was minimized by maintaining low background pressures in the shock tube and low leak rates. The present results are compared with previously published data. Using the values of the equilibrium constant, and the measured forward rate, the recombination rate has been deduced. The recombination rate is compared with some of the experimental measurements reported.