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Prediction of temperature-insensitive molecular absorption lines in laser-assisted combustion diagnostics

Walewski, Joachim LU and Elmqvist, A (2005) In Journal of Quantitative Spectroscopy & Radiative Transfer 91(4). p.415-436
Abstract
In laser-assisted combustion diagnostics it is a recurring task to predict molecular transitions whose signal strength depends only weakly on variations in temperature. The signal strength is proportional to the Boltzmann fraction of the level probed and the amplitude of the absorption line profile. In the past investigations have been presented in which this task was attack by detailed numerical calculations of the temperature dependence of pertinent physical properties of the molecule. Another widely applied approach relies on an analytical formula for the Boltzmann fraction of hetero-nuclear diatomic molecules and the neglect of line shape effects. The analytical approach experiences a continuing popularity in laser-assisted combustion... (More)
In laser-assisted combustion diagnostics it is a recurring task to predict molecular transitions whose signal strength depends only weakly on variations in temperature. The signal strength is proportional to the Boltzmann fraction of the level probed and the amplitude of the absorption line profile. In the past investigations have been presented in which this task was attack by detailed numerical calculations of the temperature dependence of pertinent physical properties of the molecule. Another widely applied approach relies on an analytical formula for the Boltzmann fraction of hetero-nuclear diatomic molecules and the neglect of line shape effects. The analytical approach experiences a continuing popularity in laser-assisted combustion diagnostics, which is why we compared both approaches with each other. The objective of this comparison was to assess the accuracy of the analytical approach and to reveal its potential pitfalls. Our comparison revealed that the analytical approach suffers from mediocre accuracy, which makes it unfit for practical applications. One cause is the neglect of higher lying vibrational levels, which show a non-negligible population for typical flame temperatures. Another reason is the neglect of fine structure splitting in molecules with non-zero orbit angular momentum in the ground state. Another reason for the observed inaccuracy is the neglect of line shape effects quenching, which were found to have a significant effect on the temperature sensitivity of a line. Because of its insufficient accuracy due to both oversimplified models of the molecular energy levels and the neglect of line shape effects and quenching we discourage from applying the analytical approach and recommend the use of detailed numerical approaches that are free of the above limitations. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
combustion diagnostics, laser spectroscopy, resonant techniques
in
Journal of Quantitative Spectroscopy & Radiative Transfer
volume
91
issue
4
pages
415 - 436
publisher
Elsevier
external identifiers
  • wos:000225346200003
  • scopus:6444229545
ISSN
0022-4073
DOI
10.1016/j.jqsrt.2004.07.002
language
English
LU publication?
yes
id
f1f138cf-cd1b-4cc4-a3aa-0fe5bc119319 (old id 259826)
date added to LUP
2007-08-22 16:52:35
date last changed
2017-01-01 07:27:29
@article{f1f138cf-cd1b-4cc4-a3aa-0fe5bc119319,
  abstract     = {In laser-assisted combustion diagnostics it is a recurring task to predict molecular transitions whose signal strength depends only weakly on variations in temperature. The signal strength is proportional to the Boltzmann fraction of the level probed and the amplitude of the absorption line profile. In the past investigations have been presented in which this task was attack by detailed numerical calculations of the temperature dependence of pertinent physical properties of the molecule. Another widely applied approach relies on an analytical formula for the Boltzmann fraction of hetero-nuclear diatomic molecules and the neglect of line shape effects. The analytical approach experiences a continuing popularity in laser-assisted combustion diagnostics, which is why we compared both approaches with each other. The objective of this comparison was to assess the accuracy of the analytical approach and to reveal its potential pitfalls. Our comparison revealed that the analytical approach suffers from mediocre accuracy, which makes it unfit for practical applications. One cause is the neglect of higher lying vibrational levels, which show a non-negligible population for typical flame temperatures. Another reason is the neglect of fine structure splitting in molecules with non-zero orbit angular momentum in the ground state. Another reason for the observed inaccuracy is the neglect of line shape effects quenching, which were found to have a significant effect on the temperature sensitivity of a line. Because of its insufficient accuracy due to both oversimplified models of the molecular energy levels and the neglect of line shape effects and quenching we discourage from applying the analytical approach and recommend the use of detailed numerical approaches that are free of the above limitations.},
  author       = {Walewski, Joachim and Elmqvist, A},
  issn         = {0022-4073},
  keyword      = {combustion diagnostics,laser spectroscopy,resonant techniques},
  language     = {eng},
  number       = {4},
  pages        = {415--436},
  publisher    = {Elsevier},
  series       = {Journal of Quantitative Spectroscopy & Radiative Transfer},
  title        = {Prediction of temperature-insensitive molecular absorption lines in laser-assisted combustion diagnostics},
  url          = {http://dx.doi.org/10.1016/j.jqsrt.2004.07.002},
  volume       = {91},
  year         = {2005},
}