Frequency modulation spectroscopy in a particle-forming environment for the detection of SiH2 Academic Article uri icon


  • © 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Frequency modulation (FM) spectroscopy using a tunable ring-dye laser has been demonstrated on the SiH2 reaction intermediate in a shock tube. The silylene radical is a critical species for the study of silane chemistry, the flame synthesis of materials, and the chemical vapor deposition of silicon. However, the detection of SiH2 using laser absorption techniques is complicated by the presence of condensing particles that are present in the flow fields of interest. 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 rQ0,4(4) line in the Ã-X(0; 2; 0)-(0; 0; 0) band. A calibration method has been developed to directly obtain the absolute absorption for individual time histories, independent of normal drift in the FM signal level. In addition to increasing sensitivity, the FM approach has eliminated signal contributions from particle formation that could previously dominate the long-time profile. Due to a dramatic reduction of beam-steering effects, the temporal resolution near time zero has been increased. Silylene absorption traces were obtained from SiH4 and Si2H6 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. The results show that kinetic-rate and lineshape-model revisions are necessary to fit the data.

author list (cited authors)

  • Crofton, M. W., & Petersen, E. L.

citation count

  • 4

publication date

  • January 2005