Effect of vibration-rotation coupling on simultaneous extraction of temperature and species concentration from vibrational CARS spectra of hot gases

• Published in: Journal of Raman spectroscopy Vol. 44; no. 10; pp. 1326 - 1329
• Main Author: Marrocco, Michele
• Format: Journal Article
• Language: English
• Published: Bognor Regis Blackwell Publishing Ltd 01.10.2013; Wiley Subscription Services, Inc
• Subjects: Approximation; coherent anti-Stokes Raman scattering; Coherent scattering; Coupling (molecular); Deviation; High temperature; laser spectroscopy; Mathematical analysis; Raman scattering; Spectra; spectroscopic techniques; Vibration
• ISSN: 0377-0486; 1097-4555
• DOI: 10.1002/jrs.4357

The coupling between vibration and rotation in light molecules changes the strength of the Raman response. From this standpoint, we consider high‐temperature molecular spectra obtained by means of coherent anti‐Stokes Raman scattering (CARS), whose spectral intensity is useful to extract thermometric information and species concentrations for applications in combustion science. In this context and unlike other studies on the subject that are exclusively focused on thermometry, the novelty of the current work lies in the determination of the mutual relationship among the free variables adopted in the analysis of CARS spectra when these do not include the effect of the vibration–rotation coupling. The relationship emerges from the comparison to a reference made of calculated vibrational spectra of nitrogen and oxygen subject to the coupling. These spectra are then fitted by means of spectra developed under the ordinary rigid‐rotor approximation that is usually adopted in any fitting procedure for such molecules. The results show that small changes of the fitted temperature correspond to larger deviations for the determination of concentrations and non‐resonant background. Copyright © 2013 John Wiley & Sons, Ltd. The coupling between vibration and rotation in light molecules changes the strength of the coherent anti‐Stokes Raman scattering in comparison to the conventional rigid‐rotor approximation. The results show that small changes of the fitted temperature correspond to larger deviations for the determination of concentrations and non‐resonant background. An example is the figure where the plot of the sum of squared differences indicates significant deviations for the physical parameters when the reference temperature is 2300 K.