Absolute Rate Coefficient of the Gas-Phase Reaction between Hydroxyl Radical (OH) and Hydroxyacetone: Investigating the Effects of Temperature and Pressure

Abstract

The rate coefficient (k1) of the reaction between hydroxyl radical and hydroxyacetone, which remained so far controversial, was determined over the temperature range 290-500 K using pulsed-laser photolysis coupled to pulsed-laser induced fluorescence (PLP-PLIF). Hydroxyl radical was generated by pulsed photolysis of H2O2 at 248 nm. The results show that at a pressure of 50 Torr He, the rate coefficient obeys a negative temperature dependence k1(T) = (1.77 ± 0.19) × 10(-12) exp((353 ± 36)/T) cm(3) molecule(-1) s(-1) for temperatures between 290 and 380 K, in good agreement with the results of Dillon et al. (Phys. Chem. Chem. Phys. 2006, 8, 236) at 60 Torr He. However, always at 50 Torr He but for the higher temperature range 410-500 K, a positive temperature dependence was found: k1(T) = (1.14 ± 0.25) × 10(-11) exp(-(378 ± 102)/T) cm(3) molecule(-1) s(-1), close to the expression obtained by Baasandorj et al. (J. Phys. Chem. A 2009, 113, 10495) for pressures of 2 and 5 Torr He but at lower temperatures, 280-360 K, where their k1(T) values are well below these of Dillon et al. and of this work. Moreover, the rate coefficient k1(301 K) determined as a function of pressure, from 10 to 70 Torr He, shows a pronounced decrease once the pressure is below ∼40 Torr He, thus explaining the disparity between the higher-pressure data of Dillon et al. and the lower-pressure results of Baasandorj et al. The pressure dependence of k1 and of its temperature-dependence below ∼400 K is rationalized by the reaction proceeding via a hydrogen-bonded prereactive complex (PRC) and a submerged transition state, such that at high pressures collisionally thermalized PRCs contribute additional reactive flux over and through the submerged barrier. The high-pressure rate coefficient data both of Dillon et al. and of this work over the combined range 230-500 K can be represented by the theory-based expression k1(T) = 5.3 × 10(-20) × T(2.6) exp(1100/T) cm(3) molecule(-1) s(-1).

Temperature-Dependent Rate Constant for the Reaction of Hydroxyl Radical with 3-Hydroxy-3-methyl-2-butanone

“…This non-Arrhenius behavior could be expected. Similarly to reaction of OH with hydroxyacetone (smallest hyrdoxyketone) 6,22 and also with aldehydes and ketones, in halocarbon wax coated and uncoated quartz reactors, respectively). Finally, the present experimental data were fitted with Arrhenius expression at T = 400 -830K and modified…”

The atmospheric oxidation of hydroxyacetone: Chemistry of activated and stabilized CH3C(O)CH(OH)OO• radicals between 252 and 298 K

“…Inspection of the observed product concentration data reveals curvature in the appearance profiles of essentially all species. Downward curvature in the MGLY data suggests loss via reaction with Cl, and possibly also with OH: Note that reaction of Cl with MGLY occurs with a slightly lower rate coefficient than does reaction of Cl with HYAC, while the OH/MGLY reaction is faster than the corresponding OH/HYAC reaction by about a factor of two . Box model simulations of the experiments (to be described in detail in a subsequent section) show that the vast majority of the CO observed is obtained from decomposition of the CH 3 C(O)CO• radical product of (R6): and thus the initial MGLY formation can be obtained from the sum of the MGLY and CO concentrations.…”

“…Note that reaction of Cl with MGLY occurs with a slightly lower rate coefficient than does reaction of Cl with HYAC, 22,44 while the OH/MGLY reaction is faster than the corresponding OH/HYAC reaction by about a factor of two. 27,28 Box model simulations of the experiments (to be described in detail in a subsequent section) show that the vast majority of the CO observed is obtained from decomposition of the CH 3 C(O)CO• radical product of (R6):…”

“…The major gas‐phase route for atmospheric HYAC loss appears to be its reaction with OH . Measurements for the rate coefficient for this reaction at 298 K fall in the range (2.8‐6.0) × 10 −12 cm 3 molecule −1 s −1 , with some (though not all) of the discrepancy apparently the result of a pressure‐ dependence to the rate coefficient.…”

“…Measurements for the rate coefficient for this reaction at 298 K fall in the range (2.8‐6.0) × 10 −12 cm 3 molecule −1 s −1 , with some (though not all) of the discrepancy apparently the result of a pressure‐ dependence to the rate coefficient. A value of ≈ 6 × 10 −12 cm 3 molecule −1 s −1 at conditions of the earth's surface is likely applicable, implying a tropospheric lifetime of about 3 days. While photolysis appears to be only a minor loss route for hydroxyacetone, removal via depositional processes may also be significant.…”