DETECTION OF THE $SiH_{2}$ BY $(A^{1}B_{1}-X^{1}A_{1})$ TRANSITION IN THE EMISSION SPECTRUM OF THE RARIFIED FLAME OF THE OXIDATION OF SILANE
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Date
1999
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Ohio State University
Abstract
This work is aimed at the detection of the active intermediates in the emission spectra of rarified flames of $SiH_{4}$ and dichlorosilane oxidation. A blackbody radiation from the solid aerosol particles markedly complicates the detection of the visible emission bands in the flames of silanes. We have shown that the application of constant electrical field reduces the amount of aerosol formed during the ignition of silanes- oxygen mixtures as well as the addition of $SF_{6}{^{a}}$. The both ways were used for decreasing the intensity of blackbody radiation. The experiments have been carried out under static and flow conditions at 293 K and total pressures in the range of 0,6 to 10 Torr. We have observed the intensive emission bands at 580, 589, 613 nm in the spectrum of the rarified flame of $SiH_{4} +SF_{6}+O_{2}$. These bands are due to the transitions $^{1}B_{1} (O, v^{1}, O)-^{1}A_{1} (O, v^{1}, O)$ of $SiH_{2} : (020)-(000), (030)-(010), (020-010)$ according to reported spectra of $SiH_{3}^{b}$ obtained under discharge conditions from $SiH_{4}$. The bands are also observed in the spectrum obtained under conditions of discharge $(SiH_{4} + O_{2})$ and yet are missing from the spectra of the oxidation of $SiH_{2}Cl_{2}$ in discharge as well as in the presence of $SF_{6} SiH_{2}$ reacts nearly with gas kinetic collision frequency with $SiH_{4}$; the reaction of $SiH_{4}$ with $O_{2}$ proceeds also rapidly leading to electronically excited SiO. These are the basic reactions of $SiH_{2}$ in $SiH_{4}$ oxidation. The emission spectra in the region 425 - 530 nm of the rarified flames under static conditions appear at $[SF_{6}] > 40\%$ to total pressure for $SiH_{4}$ oxidation and $[SF_{6}]> 10\%$ for $SiH_{2}Cl_{2}$ oxidation. The equidistant $(\sim 1200 cm^{-1})$ bands are common for the both reactions. This emission is caused by electronically excited $H_{2}SiO^{\ast}$ particles in accordance with theoretical $calculations^{c}$.
Description
$^{a}$ N.M. Rubtsov, V.I. Chernyah, G.I. Tsvetkov, Kinet. Catal. 38, 498, (1997) $^{b}$ I.Safarik, V. Sandhu, E.M. Lown et. al. Res.on Chem Intermed, 14, 105, (1990) $^{c}$ R.J. Glinski, J.L. Gole, D.A. Dixon.J.Am.Chem.Soc., 107, 5891, (1985)
Author Institution: Institute for Structural Macrokinetics RAS, Russia, Moscow region
Author Institution: Institute for Structural Macrokinetics RAS, Russia, Moscow region