UNIMOLECULAR DECOMPOSITION OF SIH4, SIH3F, AND SIH2F2 AT HIGH-TEMPERATURES

The thermal decomposition of SiH4, SiH3F, and SiH2F2 diluted in AR was studied behind incident shock waves by monitoring Ir emission from these reactant molecules. The rate constants of the unimolecular decomposition for all of three molecules were found to be in the pressure falloff region over the present experimental conditions (T = 1190-2150 K and P = 0.2-1.6 atm). The activation energies of measured rate constants were compared with heats of reactions for the various possible pathways for the thermal decomposition of these molecules and it was concluded that three-center H-2 elimination reactions were the dominant pathways for unimolecular reactions of SiH4-n(F)n (n = 0, 1, and 2). These rate constants decrease with increasing number of fluorine atoms, n, in SiH4-n(F)n. RRKM falloff calculations have been performed to examine the effect of fluorine substitution on the unimolecular decomposition rates of these molecules.