ARAS MEASUREMENTS ON THE THERMAL-DECOMPOSITION OF SILANE

In the present investigation the thermal dissociation of silane was measured behind reflected shock waves using the Atomic Resonance Absorption Spectroscopy (ARAS) for detecting Si, H, and O atoms. The experiments were performed at temperatures 1250 K less-than-or-equal-to T less-than-or-equal-to 2115 K and pressures between 0.7 and 1.5 bar. Initial mixtures of 0. 1 5 to 5 ppm SiH4 diluted in Ar and 5 ppm SiH4 with 500 ppm O2 diluted in Ar were studied. The H atom measurements show formation rates, which are much less than the respective rates for Si atom formation. This indicates that the H atoms were formed by secondary reactions and are not primary dissociation products of silane or silylene. A reaction mechanism suitable to describe all measured H atom concentration profiles is given in this paper. Si atoms also measured during the silane thermal decomposition were found to be useful to understand the kinetics of this process. From the Si concentration profiles together with computer simulations rate coefficients for the reactions SiH4 + M half arrow right over half arrow left k1 SiH2+H-2+M (R1) SiH2 + M half arrow right over half arrow left k1 Si+H-2+M (R2) were derived, which can be summarized by the following Arrhenius expressions: k1 = 9.9 x 10(15) exp (-24000 K/T) cm3 mol-1 S-1 k2 = 9.1 x 10(13) exp (-15100 K/T) cm3 mol-1 S-1 In the case of the SiH4/O2/Ar mixtures no detectable Si atom concentrations were found, while the observed O atom formation rates were identical to that of Si atoms in mixtures without O2 under comparable reaction conditions. This means that Si originating from the thermal decomposition of silane is directly converted into O by reaction with O2, i.e. O is in this system a measure of Si.