HIGH-TEMPERATURE KINETICS OF SI ATOM OXIDATION BY NO BASED ON SI, N, AND O ATOM MEASUREMENTS

In the present investigation the well-known high-temperature thermal decomposition of silane was used as Si atom source. Its oxidation by NO was studied behind reflected shock waves in SiH4/NO/Ar systems by applying the atomic resonance absorption spectroscopy (ARAS) technique for detecting Si, N, and O atoms. Initial mixtures of 0.5-10 ppm SiH4 and 75-300 ppm NO in Ar were used to perform experiments in the temperature range 1660 K less-than-or-equal-to T less-than-or-equal-to 3360 K at pressures 0.4 bar less-than-or-equal-to p less-than-or-equal-to 1.5 bar. From the measured Si atom absorption profiles the rate coefficient for the reaction Si + NO half arrow right over half arrow left SiO + N (R3), k3, was determined by applying the first-order method, which is known to be independent of calibration. The results were summarized by the Arrhenius expression k3 = 3.2 X 10(13) exp(-1775 K/T) cm3 mol-1 S-1(+/- 40%). To confirm the correctness of reaction R3, N atoms were also measured in the SiH4/NO/Ar system. In that case the formation of N atoms via reaction R3 and the consumption by reaction with NO, N + NO half arrow right over half arrow left N2 + O (R4), was observed. By computer simulations all measured N atom concentrations were fitted to the calculated ones by varying the rate coefficient k4. A temperature-independent value of k4 = 2.0 x 10(13) cm3 mol-1 s-1 (+/- 50%) was obtained. Finally, O atoms were measured in the SiH4/NO/Ar system. All O atom profiles observed were well fit by computer simulations based on a reaction scheme containing the dissociation of silane, reactions of Si and N with NO, and the well-known O + H-2 half arrow right over half arrow left OH + H reaction.