A comparative study of the reactivity of the silicon atom Si(3PJ) towards O2 and NO molecules at very low temperature

Abstract

We present both an experimental and a theoretical study of the reactions Si(³P_J) + O₂ and Si(³P_J) + NO. The CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) experimental technique is used to measure the rate constants in the temperature range 15–300 K. The laws of variation of the rate constants as a function of temperature are found to exhibit a maximum around 30 K for both reactions and are experimentally described using the following expressions: k_Si+O2(T) = (1.72 ± 0.17) × 10⁻¹⁰ (T/300 K)^{−(0.53±0.10)}exp^{−(17±4)K/T} cm³ molecule⁻¹ s⁻¹ and k_Si+NO(T) = (0.90 ± 0.10) × 10⁻¹⁰(T/300 K)^{−(0.96±0.10)}exp^{−(28±3)K/T} cm³ molecule⁻¹ s⁻¹. Adiabatic capture calculations are also performed and the temperature dependences obtained for the rate constants present a maximum in good agreement with the experimental results. A perturbative approach is eventually used in the limit of zero temperature to differentiate the spin–orbit reactivity of the silicon atom. These results are also compared with an earlier similar study concerning the reactivity of carbon atoms in the ground state, C(³P_J), with the same molecules.