Rate Constant of the Reaction of OH Radicals with HBr over the Temperature Range 235-960 K

The kinetics of the reaction of hydroxyl radicals with HBr, important in atmospheric and combustion chemistry, has been studied in a discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer in the temperature range 235-960 K. The rate constant of the reaction OH + HBr -> H2O + Br (1) was determined using both a relative rate method (using the reaction of OH with Br-2 as a reference) and absolute measurements, monitoring the kinetics of OH consumption under pseudo-first-order conditions in excess of HBr. The observed U-shaped temperature dependence of k(1) is well represented by the sum of two exponential functions: k(1) = 2.53 x 10(-11) exp(-364/T) + 2.79 x 10(-)(13) exp(784/T) cm(3) molecule(-1) s(-1) (with an estimated conservative uncertainty of 15% at all temperatures). This expression for k(1), recommended for T = 240-960 K, combined with that from previous low temperature studies, k(1) = 1.06 x 10(-11) (T/298)(-0.9) cm(3) molecule-1 s(-1) at T = 23-240 K, allows to describe the temperature behavior of the rate constant over an extended temperature range 23-960 K. The current direct measurements of k(1) at temperatures above 460 K, the only ones to date, provide an experimental dataset for use in combustion and volcanic plume modeling and an experimental basis to test theoretical calculations.

Automated summary

In this study, the kinetics of the reaction between hydroxyl radicals and HBr were investigated using various methods, and a temperature-dependent rate constant expression was determined. The results provide an experimental dataset for atmospheric and combustion chemistry modeling.