Quantitative evaluation of vibrational excitation of SiO A(1)Pi-X-1 Sigma(+) flame emission from a silane/hydrogen/oxygen/argon diffusion flame

Spontaneous emission spectra in the wavelength range from 200 to 420 nm fro m a SiH4/H-2/O-2/Ar diffusion flame (used for the synthesis of nanosized pa rticles) were obtained. Si, SIH and SiO intermediates were identified from the spectral emission signature. Emission from the SiO A(1)Pi-X(1)Sigma(+) transition was analyzed in detail. Comparison of the experimental data with an emission model for SiO indicated significant vibrational non-equilibriu m. The level of vibrational excitation was quantified in terms of a vibrati onal temperature independent of a translational temperature, The best-fit m odel results obtained by comparison with the experimental data, yielded a t ranslational temperature of T-trans = 3250 +/- 500 K and a vibrational temp erature of T-vib = 15 000 +/- 5000 K for high oxygen concentration systems. The vibrational temperature corresponds to an energy equivalent of similar to 29 kcal/mol and changes in fractional population of over an order of ma gnitude from equilibrium distributions for some vibrational levels. For low oxygen concentration systems, the vibrational temperature was significantl y higher T-vib = 40000 +/- 15000 K, which indicates a different SiO formati on mechanism is active for these conditions. (C) 1999 Elsevier Science Ltd. All rights reserved.