Rate coefficients for the reactions of Si(3PJ) with C2H2 and C2H4: Experimental results down to 15 K

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.