The Kinetic Coefficient of the C₂H₄ + O Reaction Over Extended Pressure and Temperature Ranges

Summary

A model suggested by Hunziker et al. (6) to explain the pressure dependence of the product distribution of the C₂H₄ + O reaction also implies pressure dependence of the total rate constant k₁ of the reaction. The aim of the present study was to measure the rate constant k in the pressure ränge of 0.5 to 5 torr, at temperatures from 300 to 850 K and to compare the results with those obtained at 26–200 torr by other investigators. Using the discharge-flow technique, the rate constant was determined from the exponential decay of C₂H₄ at a large excess of O-atoms. Species concentrations were monitored by mass spectrometry using line-of-sight sampling; the sensitivity for 0 was determined on the basis of the NO + N reaction. Our k₁ results show no evidence for pressure dependence in the 0.5 to 5 torr ränge; moreover they agree very closely with the values obtained by other workers at 26–200 torr. The experimental results are at variance with the Hunziker model, which, as shown by RRKM calculations, would imply marked fall-off of k₁ in the 0.5 to 200 torr range, at least at higher temperatures.