Rates of reaction of alkyl radicals with ozone

The rate constants for a series of alkyl radicals reacting with ozone have been measured at 298 K and 2 torr by using a photoionization mass spectrometer. The radical (R) + ozone rate constants (in units of 10/sup -12/ cm/sup 3/ molecule/sup -1/ s/sup -1/) are 2.53 +/- 0.54 for CH/sub 3/, 25.3 +/- 5.8 for C/sub 2/H/sub 5/, 24.4 +/- 5.9 for 1-C/sub 3/H/sub 7/, 46.5 +/- 10.6 for 2-C/sub 3/H/sub 7/, and 54.5 +/- 11.4 for t-C/sub 4/H/sub 9/. As was observed for the R + O/sub 2/ reactions the R + O/sub 3/ reactions show a trend of increasing rate constant k/sub 1/ with decreasing ionization potential (IP) of the radical. When log (k/sub 1/) vs. IP(R) - EA(O/sub 2/ or O/sub 3/) is plotted, where EA represents electron affinity, the two families of rate constants are brought into close proximity. In addition, rate constants for fluorescence quenching of substituted benzenes by O/sub 2/ are cited which extend the log (k) vs. IP-EA plot to lower ionization potential. Adiabatic channel model calculations have been done by using a long-range potential resulting from the perturbation between the R/sup +/ + O/sub 3//sup -/ and R + O/sub 3/ surfaces. These calculations give good agreement with the experimental cross sections and they predict rate constants faster than those derived from the classical harpoon model at low IP-EA.