Dissociation of Br2 in shock waves

Abstract

The rate of dissocation of Br2 in the presence of Ar and Br2 has been investigated using three independent experimental techniques in the same shock tube: molecular absorption spectroscopy (AS), two-body emission spectroscopy (ES), and laser schlieren technique (LS). Present results yield recombination rate constants in good agreement with each other and with earlier high temperature flash photolysis data. The temperature range over which dissociation was studied was extended from 1200 to 3000 °K. Recombination rate constants can be summarized in terms of the following equations: log10krAr(LS) =8.251(±0.002)−1.36(±0.29)log10(T/2300) or log10krAr(LS) =8.378(±0.001)−1.05(±0.30) log10(T/2300). The difference between these two equations arose because in the first equation RBr=RBr2 was assumed, while in the second RBr=RKr was used. Here Rx is the Gladstone–Dale constant of X. These equations are valid between 1600 and 3000°K. The analogous equations for krBr2 are: log10kBr2=8.718(±0.001)−2.35(±0.41)log10(T/1900) and log10krBr2=8.767(±0.001)−2.18(±0.42) log20(T/1900), valid between 1600 and 2000 °K. Furthermore, it is found that log10krAr(AS+ES) =8.182(±0.003)−1.42(±0.18)log10(T/1963), valid between 1180 and 2890 °K. The laser schlieren technique, as applied to chemical reactions in shock waves, was studied. In particular, the effect of finite width laser beam, optical absorption of reacting gas, temperature dependence of its refractive index, and composition dependence of its Gladstone–Dale constant, were investigated. It was found that calculated values of rate constants are sensitive functions of refraction, and hence polarizabilities, of reaction products. Although generally these properties are not known, they can be estimated empirically.