Application of the FM spectroscopic technique to SiH2 detection in a shock tube
Frequency modulation (FM) spectroscopy using a tunable ring-dye laser has been demonstrated on the SiH2 reaction intermediate in a shock tube. In the present application of FM spectroscopy, the modulation frequency is higher than normally employed, allowing one sideband to be well off the peak despite the broad lineshape of the rQo,4(4) line in the \( \tilde A - \tilde X \) (0,2,0)–(0,0,0) band. In addition to increasing sensitivity, the FM approach has eliminated signal contributions from particle formation that previously could dominate the long-time pro- file. Silylene absorption traces were obtained from SiHU mixtures highly diluted in argon and reflected-shock heated to temperatures between 1070 and 1610 K. Minimum detection sensitivities well below 0.05% absorption were demonstrated, corresponding to < 0.1 ppm SiH2.
KeywordsFrequency Modulation Shock Tube Soot Formation Laser Absorption Reflect Shock Wave
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