Kinetic Study of the Gas-Phase Reaction of OH with Br₂

Abstract

An experimental, temperature-dependent kinetic study of the gas-phase reaction of the hydroxyl radical with molecular bromine (reaction 1) has been performed using a pulsed laser photolysis/ pulsed-laser-induced fluorescence technique over a wide temperature range of 297 -766 K, and at pressures between 6.68 and 40.29 kPa of helium. The experimental rate coefficients for reaction 1 demonstrate no correlation with pressure and exhibit a negative temperature dependence with a slight negative curvature in the Arrhenius plot. A non-linear least-squares fit with two floating parameters of the temperature dependent k 1 (T) data set using an equation of the form k 1 (T) = AT n yields the recommended expression k 1 (T) = 1.85×10 −9 T − 0.66 cm 3 molecule −1 s −1 for the temperature dependence of the reaction 1 rate coefficient. The potential energy surface (PES) of reaction 1 was investigated using quantum chemistry methods. The reaction proceeds through formation of a weakly bound OH···Br 2 complex and a PES saddle point with an energy below that of the reactants. Temperature dependence of the reaction rate coefficient was modeled using the RRKM method on the basis of the calculated PES.

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

“…This reaction is very often used in our laboratory for indirect detection of OH by mass spectrometry via conversion of the radicals to HOBr 10−12 and as a reference reaction in the relative measurements of OH reactivity 13,14 The rate constant of the reaction seems to be well established at low temperatures (T = 230−360 K); 15,16 however, only one temperature dependence study is available at higher temperatures. 17 In the present work, we report the measurements of the rate constant in an extended temperature range, T = 220− 950 K.…”

Inhibition of hydrogen oxidation by HBr and Br2

“…Despite recent regulations, brominated flame retardants are still an ingredient in many materials, and bromine reactions continue to be a concern in relation to waste incineration processes [2,3]. Due to the interaction of bromine species with the combustion process and with other trace species, there is a renewed interest in the elementary reactions of bromine species, in particular at higher temperatures [4]. The presence of bromine species may enhance or inhibit fuel oxidation, depending on the reaction conditions [5].…”

Kinetics and Products of the Reaction of OH Radicals with ClNO from 220 to 940 K

“…k 3 = (1.85 × 10 -9 )×T -0.66 cm 3 molecule -1 s -1 (T = 297 -766 K). 10 This reaction was also used for the determination of the absolute concentrations of OH…”