Rates of reaction of hydroxyalkyl radicals with molecular oxygen

The rate constants for the reactions of a series of hydroxyalkyl radicals with molecular oxygen have been measured at room temperature (296 ± 4 K) by laser flash photolysis-photoionization mass spectrometry. Measured rate constants are k[CH₂OH+O₂] = (1.17 ± 0.12) × 10^-11, k[CH₃CH₂CHOH+O₂] = (2.61 ± 0.41) × 10^-11, k[CH₃CHCH₂OH+O₂] = (1.16 ± 0.22) × 10^-11, k[CH₃CH(OH)CH₂H-O₂] = (3.82 ± 0.60) × 10^-12, and k[CH₃C(OH)CH₃+O₂] = (3.71 ± 0.62) × 10^-11, all in units of cm³ molecule^-1 s^-1. These reactions seem to be at high-pressure limits at experimental pressures (1.3-5.5 Torr of He). Although it has been suggested in previous studies that the reaction mechanisms are different between α- and β-hydroxyalkyl radicals (H atom abstractions and recombinations, respectively), the present rates of reaction involving both α- and β-hydroxyalkyl radicals were found to correlate well with the ionization potentials of the radicals. This result suggests that the rate constants for all these reactions are largely controlled by the long-range forces similar to the reactions of alkyl radicals with molecular oxygen.