On the quantification of OH*, CH*, and C2* chemiluminescence in flames

Abstract  
Absolute concentrations of all important chemiluminescent species, OH–A, CH–A, CH–B, and C2-d have been measured for the first time in methane-oxygen flames at low pressure. The optical detection system for chemiluminescence
measurements has been calibrated with Rayleigh and Raman scattering of a cw laser, with the latter approach yielding superior
results.
The measured ratio between the concentration of CH–B and CH–A suggests that the electronically excited CH* is formed close
to thermal equilibrium. Introduction of different rate constants for reactions leading to CH–A and CH–B were not necessary
to explain the experimental results. Results are compared with a recent numerical model. Deviations in profile shape and peak
positions are relatively small for stoichiometric flames, but become more pronounced in richer mixtures. Larger discrepancies
are observed for the absolute concentrations, depending on the chemiluminescent species and the stoichiometry.
In an attempt to find an alternative method for the quantification of chemiluminescent species, MIR-CRDS has been performed
around 3.9 μm. While H2O and OH–X could be measured, the sensitivity was not high enough to detect the low sub-ppb concentration of OH–A—in part
due to the limited reflectivity of mirrors in the MIR, in part due to a significant background of hot H2O lines.

  • Content Type Journal Article
  • Pages 1-9
  • DOI 10.1007/s00340-012-5006-9
  • Authors
    • P. Nau, Physikalische Chemie 1, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld, Germany
    • J. Krüger, Physikalische Chemie 1, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld, Germany
    • A. Lackner, Physikalische Chemie 1, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld, Germany
    • M. Letzgus, Physikalische Chemie 1, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld, Germany
    • A. Brockhinke, Physikalische Chemie 1, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld, Germany

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