Pressure dependence of two relative ozone formation rate coefficients

The large enrichment observed in many ozone isotopomers has a pronounced pressure and temperature dependence and has been traced to rate coefficient advantages of certain formation channels. The pressure dependence of two relative rate coefficients 16O+18O18O/16O+16O16O and 18O+16O16O/18O+18O18O has been investigated. The first coefficient decreases as the ozone formation pressure increases from 40 to 3000 Torr, while the second remains unchanged. Reaction 16O+18O18O which has a 50% higher rate of formation than 18O+16O16O is therefore responsible for the decrease in isotope enrichment as the pressure of ozone formation increases.