Quantitative evaluation of vibrational excitation of SiO A 1Π–X 1Σ + flame emission from a silane/hydrogen/oxygen/argon diffusion flame

Abstract

Spontaneous emission spectra in the wavelength range from 200 to 420 nm from a SiH 4/H 2/O 2/Ar diffusion flame (used for the synthesis of nanosized particles) were obtained. Si, SiH and SiO intermediates were identified from the spectral emission signature. Emission from the SiO A 1Π–X 1Σ + transition was analyzed in detail. Comparison of the experimental data with an emission model for SiO indicated significant vibrational non-equilibrium. The level of vibrational excitation was quantified in terms of a vibrational temperature independent of a translational temperature. The best-fit model results obtained by comparison with the experimental data, yielded a translational temperature of T trans=3250±500 K and a vibrational temperature of T vib =15 000±5000 K for high oxygen concentration systems. The vibrational temperature corresponds to an energy equivalent of ∼29 kcal/mol and changes in fractional population of over an order of magnitude from equilibrium distributions for some vibrational levels. For low oxygen concentration systems, the vibrational temperature was significantly higher T vib =40 000±15 000 K, which indicates a different SiO formation mechanism is active for these conditions.