Kinetics of the Reaction of O(3P) Atoms with Benzene

Abstract

The kinetics of the gas phase reaction of O(³P) atoms with benzene was investigated using fast flow techniques. Specific rate constants were obtained using two separate systems, one with ESR detection to monitor the decrease in O(³P) atoms and the other with mass spectrometry to follow the change in benzene concentration. The rate constant computed with respect to O(³P) removal is much larger than that obtained in the mass spectrometer studies and this is believed to result from further reactions of oxygen atoms with radical species produced in the initial O(³P)+C₆H₆ interaction. On the basis of the mass spectrometric studies a specific rate constant for the reaction $$\mathrm{O}{(}^3\mathrm{P)+}{\mathrm{C}}_6{\mathrm{H}}_6\mathrm{\to \; [}{\mathrm{C}}_6{\mathrm{H}}_6\mathrm{O}]$$ of ${\text{(3.8± 1.5) × 10}}^{13}\hspace{0.17em}\exp \text{(−4,400± 500/RT)\hspace{0.17em}}{\mathrm{cm}}^3\hspace{0.17em}{\mathrm{mole}}^{\text{−1}}·{\sec }^{\text{−1}}$ was obtained over the temperature range of 255–305°K. A negligibly small kinetic isotope effect was observed in competitive experiments with C₆H₆ and C₆D₆. The results obtained are interpreted in terms of a rate determining step involving the addition of oxygen atoms to the benzene ring followed by subsequent isomerization and/or decomposition reactions.