The temperature dependence of the rate coefficient for the reaction, OH + HBr has been reinvestigated at low temperatures (T = 48-224 K) by using uniform supersonic flow reactors with laser induced fluorescence detection. This paper presents two forms of global fits: k(T) = 1.11 × 10 −11 (T/298) −0.91 cm 3 s −1 and k(T) = 1.06 × 10 −11 (T/298) −1.09 exp( −10.5 K T ) cm 3 s −1 , both of which accurately describe the temperature dependence of the rate coefficient for the title reaction within the temperature range 20-350 K. These fits indicate that at temperatures below 200 K, the rate coefficient for this reaction shows inverse temperature dependence, while above 200 K the reaction shows insignificant temperature dependence.

Rate coefficients for the reaction of ground-state silicon atoms Si(3PJ) with acetylene and ethylene have been measured at temperatures down to 15 K. The experiments have been performed in a continuous flow CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus using pulsed laser photolysis of Si(CH3)4 to generate Si(3PJ) atoms and laser-induced fluorescence to observe the kinetic decay of the atoms and hence determine the rate coefficients. Both reactions are found to be fast, and the reaction rates show a very mild dependence on temperature. The rate coefficients match the expressions k(Si+C2H2)=(2.6±0.6)10−10(T/300)−(0.71±0.24) exp(−(29±10)/T) cm3 molecule−1 s−1 and k(Si+C2H4)=(3.7±0.3)10−10(T/300)−(0.34±0.10) exp(−(16±4)/T) cm3 molecule−1 s−1 in the temperature range 15–300 K. The nature of the products and the similarities of the carbon and silicon chemistry are discussed.