Re-evaluation of rate coefficients for ozone decomposition by oxygen in wide range of gas pressures (20–1000 Torr) and temperatures (293–423 K)

Abstract

The effective lifetime of ozone in a cylindrical cell filled with oxygen was measured in a wide range of gas pressures and temperatures by the HgI photoabsorption method. The observed effective lifetime of ozone increased with the gas pressure from 20 to 500 Torr, reached a maximum at approximately atmospheric pressure and then decreased in inverse proportion to the gas pressure. These characteristics were investigated at temperatures of 293–423 K and good agreement was observed with theoretical results derived by diffusion equation analysis of the ozone concentration in the photoabsorption cell. From the gas pressure and temperature dependencies of the effective lifetime of ozone, the diffusion coefficient of ozone in oxygen was determined together with the reflection coefficient of ozone at the surface, which was used to derive the loss rate of ozone at the surface of the cell at low gas pressures below 200 Torr. Moreover, we also simultaneously determined the rate coefficients for the decomposition of ozone by collisions with oxygen molecules and atoms which were used to derive the loss rate of ozone in the gas phase at high gas pressures of above 200 Torr. We have revealed that the Arrhenius plots, expressing the observed rate coefficients, comprised two linear portions with different slopes that transitioned from one to the other at around 353 K. Considering that the two trends reflected the decomposition of ozone by interactions with molecular and atomic oxygen, we obtained coefficients k(O2) and k(O) taking into account the diffusion effect of ozone molecules. We derived the rate coefficient k(O2) = 7.28 × 10−14exp(−9300/T) (cm3 s−1) as a re-evaluated value in the present paper and k(O) = 9.52 × 10−12exp(−2080/T) (cm3 s−1) which was consistent with data compiled in the original databases.