Flash photolysis resonance fluorescence investigation of the gas-phase reactions of hydroxyl radicals with a series of aliphatic ketones over the temperature range 240-440 K

Abstract

Absolute rate constants have been determined for the gas-phase reactions of OH radicals with a series of aliphatic ketones by the flash photolysis resonance fluorescence measurement technique. Experiments were performed over the temperature range 240-440 K at total pressures (using Ar diluent gas) between 25 and 50 Torr. The rate constant data for acetone (k/sub 1/), 2-butanone (k/sub 2/), and 3-pentanone (k/sub 3/) were used to derive the Arrhenius expressions k/sub 1/ = (1.7 +/- 0.4) x 10/sup -12/ exp(-(600 +/- 75)/T) cm/sup 3/ molecule/sup -1/ s/sup -1/, k/sub 2/ = (2.3 +/- 1.1) x 10/sup -12/ exp(-170 +/- 120)/T) cm/sup 3/ molecule/sup -1/ s/sup -1/, and k/sub 3/ = (2.8 +/- 0.3) x 10/sup -12/ exp(10 +/- 35)/T) cm/sup 3/ molecule/sup -1/ s/sup -1/. At 296 K, the measured rate constants (in units of 10/sup -13/ cm/sup 3/ molecule/sup -1/ s/sup -1/) were k/sub 1/ = 2.16 +/- 0.16, k/sub 2/ = 11.5 +/- 1.0, and k/sub 3/ = 27.4 +/- 1.3. Room temperature rate constants for the reaction of OH radicals with a number of other 2-ketones were also determined. These were (in the above units) 3,3-dimethyl-2-butanone (12.1 +/- 0.5), 2-pentanone (40.0 +/- 2.9), 2-hexanone (66.4 +/- 5.6),more » 2-heptanone (86.7 +/- 8.4reverse arrow, 2-octanone (110 +/- 9), 2-nonanone (122 +/- 13), and 2-decanone (132 +/- 12). The error limits represent 2 standard deviations (from the least-squares analysis); the authors estimate that an additional 5% uncertainty should be added to account for possible systematic error in the measurements. These results are discussed in terms of reactivity trends for C-H bonds located in the ..cap alpha.., ..beta.., and ..gamma.. positions with respect to the carbonyl group.« less