COMPARATIVE RATES OF EXCHANGE BEHIND REFLECTED SHOCK-WAVES .1. (CO)-O-18 VS (CO)-C-13 + CO2

The rate of exchange of carbon monoxide with carbon dioxide was studied over the temperature range 3060-4115 K by analyzing the gas from the reflected shock zone at 20-μs intervals with a time-of-flight mass spectrometer. Separate mixtures containing 2% C18O-2% CO2 and 2% 13CO-2% CO2 each diluted with inert gas were sampled dynamically in order to measure the time dependence of a major product, m/e 46 or m/e 45. The time dependence was determined to be nonlinear for both mixtures. However, the rate of formation of m/e 46 exceeded that of m/e 45 over the range covered. Computer simulation of the respective product profiles using the appropriate atomic mechanism failed to account for the total amount of exchange conversion observed. A molecular mechanism involving excitation of reactants prior to the transition state leading to exchange is proposed. Two molecular channels involving three and four center transition state geometries participate. © 1978 American Chemical Society.