Previous studies have shown a significant OH yield from the reaction of RCO radicals (generated from the photolysis of corresponding ketone) with oxygen below total pressures of 200 Torr. The potential of these reactions as a source of OH radicals for flash photolytic kinetic studies is investigated. The viability of the method was tested by measuring rate coefficients for the reaction of OH with ethanol using both acetone/O 2 mixtures and t-butyl hydroperoxide photolysis. The results (with statistical errors at the 2σ level) are in excellent agreement with each other (k EtOH (acetone) = (5.87 ± 0.34) × 10 −18 T 2 exp((515 ± 21)K/T ) cm 3 molecule −1 s −1 and k EtOH (t-butyl hydroperoxide) = (5.27 ± 0.34) × 10 −18 T 2 exp((557 ± 20)K/T ) cm 3 molecule −1 s −1 ) and with the IUPAC recommendation. The reaction of OH with methyl ethyl ketone (2-butanone) has also been investigated using a similar technique. The results show a strong non-Arrhenius temperature dependence, k = (3.84 ± 0.12) × 10 −24 × T 4 × exp((1038 ± 11)/T ). The merits of the ketone/oxygen OH source are contrasted with other established precursors. A major advantage of the technique is the ability to cleanly generate OD without the potential for isotopic scrambling prior to photolysis. C

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