Very Low Pressure Reactor Study of the H + HBr ->/<- H2 + Br Reaction

Article abstract of DOI:10.1021/j100046a023

The reaction of H atoms, generated by microwave discharge of H2/Ar gas mixtures, with HBr has been studied employing the very low pressure reactor (VLPR) technique.Reactants and reaction products were followed by mass spectrometry.Rate constants of (5.4 +/- 0.7) x 1E-12, (6.3 +/- 0.8) x 1E-12, and (6.8 +/- 0.4) x 1E-12 cm³ molecule^-1 s^-1 were extracted for the title reaction at 268, 298, and 333 K, respectively.Difficulties were encountered in obtaining mass balance closure for molecular hydrogen, owing to its production from the internal surfaces of the phosphoric acid coated quartz microwave tube.Formation of very small amounts of molecular bromide, detected at m/e 158, 160, and 162, appeared due to some back-diffusion of HBr into the microwave tube.Br2 formation was observed to be a function of discharge power and, at sufficiently high powers, could be reduced below detection limits.Under these conditions, bromine mass balances (Br2, Br, and HBr)were around (95 +/- 5)percent.A transtion state calculation provides an estimated preexponential factor for the reaction in good agreement with our experimental results and with those available from the other most recent temperature-dependent studies.The temperature dependence of reaction 1 can be expressed by k₁/cm³ molecule ^-1 s^-1 = 9.96 x 1E-13T^0.5 exp(-300/T) over the temperature range 200-1000 K.