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Proceedings Paper

Collisional Narrowing Effects In The Raman Q-Branch Spectral Profiles Of N[sub]2[/sub], Co, And NO.
Author(s): W. S. Hurst; G. J. Rosasco; W. Lempert
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Paper Abstract

High resolution (10 MHz) stimulated Raman Q-branch spectra of molecules important in combustion are reported. In addition to the normal linear pressure broadening, line interference which leads to collisional narrowing is demonstrated. If proper account is not taken of this latter effect, large errors in the temperature and/or pressure as extracted from the spectral profile can result. The formalism which describes the spectrum and accounts for both line broadening and line interference effects is reviewed. The resulting ("relaxation") matrix equation (NxN for an N-line spectrum) can be reduced by means of a perturbation solution to a spectral distribution involving a line-broadening coefficient and a line-interference coefficient for each line. This approach is applied successfully for the spectra of N2 and CO. Further, it is shown that for the simple diatomics the J-dependent line broadening/interference coefficients can be expressed in terms of simple scaling/fitting laws for the rates of rotationally inelastic collisions. The use of fitting laws leads to a simple parameterization of all the elements of the relaxation matrix and therefore allows a determination of the spectrum. This latter approach is applied to the analysis of the Q-branch spectrum of NO, for which the perturbation solution cannot be applied because of the nearly degenerate Q-branch lines arising from its two ground state electronic configurations. It is shown that collisional narrowing in the NO Q-branch spectrum is reproduced quite well by employing a fitting law model.

Paper Details

Date Published: 28 June 1984
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Proc. SPIE 0482, Applications of Laser Chemistry & Diagnostics, (28 June 1984); doi: 10.1117/12.943099
Show Author Affiliations
W. S. Hurst, National Bureau of Standards (United States)
G. J. Rosasco, National Bureau of Standards (United States)
W. Lempert, NASA Langley Research Center (United States)


Published in SPIE Proceedings Vol. 0482:
Applications of Laser Chemistry & Diagnostics
Albert B. Harvey, Editor(s)

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