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

Abstract

Reactions of hydroxyketones with OH radicals are of importance in atmospheric chemistry and represent a theoretical interest because they proceed through two reaction pathways, formation of a hydrogen-bonded prereactive complex and direct H-atom abstraction. In this work, the kinetics of the reaction of OH radicals with 3-hydroxy-3-methyl-2-butanone (3H3M2B) has been investigated at 2 Torr total pressure of helium over a wide temperature range, T = 278-830 K, using a discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer. The rate constant of the reaction OH + 3H3M2B → products (1) was determined using both a relative rate method and absolute measurements under pseudo-first-order conditions, monitoring the kinetics of OH consumption in excess of 3H3M2B, k1= 5.44 × 10-41T9.7exp (2820/T) and 1.23 × 10-11 exp (-970/T) cm3 molecule-1 s-1 at T = 278-400 and 400-830 K, respectively (with a total uncertainty of 20% at all temperatures). The rate constant of the reaction OH + Br2 → HOBr + Br (2) was measured as a part of this study using both absolute and relative rate methods: k2 = 2.16 × 10-11 exp (207/T) cm3 molecule-1 s-1 at T = 220-950 K (with conservative 10% uncertainty). The kinetic data from the present study are discussed in comparison with previous measurements and theoretical calculations.