Rate constants for the reaction of atomic and molecular bromine with gallium arsenide

The reaction of the (100) face of a gallium arsenide single crystal with atomic and molecular bromine has been studied in a discharge flow system at temperatures between 100 and 225°C and pressures between 0.1 and 40 torr. The reaction with Br 2 was found to be first order in Br 2 only at pressures below 1 torr. Temperature dependence studies in the linear range gave the activation energy and preexponential factor for the rate controlling reaction in the low pressure regime. The results are summarized in the following Arrhenius equation:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = 10^{\left({4.5 \pm 5} \right)} \mu {\rm m}\ {\rm min}^{- 1}\ {\rm torr}^{- 1} e^{- {{\left({26.6 \pm 4.2{{{\rm kJ}} \mathord{\left/ {\vphantom {{{\rm kJ}} {{\rm mol}}}} \right. \kern-\nulldelimiterspace} {{\rm mol}}}} \right)} \mathord{\left/ {\vphantom {{\left({26.6 \pm 4.2{{{\rm kJ}} \mathord{\left/ {\vphantom {{{\rm kJ}} {{\rm mol}}}} \right. \kern-\nulldelimiterspace} {{\rm mol}}}} \right)} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} $$\end{document}Deviations from linearity at high pressures are discussed in terms of two alternative mechanisms. The reaction of GaAs with atomic bromine was also studied as a function of temperature, and found to have a temperature dependence described by the following Arrhenius equation:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_3 = \left({2.0 \pm 0.5} \right) \times 10^4 \mu {\rm m}\ {\rm min} ^{- 1}\ {\rm torr}^{- 1} e^{- {{\left({12.9 \pm 0.9} \right){\rm kJ}} \mathord{\left/ {\vphantom {{\left({12.9 \pm 0.9} \right){\rm kJ}} {{{{\rm mol}} \mathord{\left/ {\vphantom {{{\rm mol}} {RT}}} \right. \kern-\nulldelimiterspace} {RT \right. \kern-\nulldelimiterspace} {{{{\rm mol}} \mathord{\left/ {\vphantom {{{\rm mol}} {RT}}} \right. \kern-\nulldelimiterspace} {RT $$\end{document}