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Herman–Wallis correction in vibrational CARS of oxygen


  • This article is part of the Journal of Raman Spectroscopy special issue entitled “Proceedings of the 9th European Conference on Nonlinear Optical Spectroscopy (ECONOS), Bremen, Germany, June 21-23, 2010” edited by Peter Radi, PSI, Villigen, Switzerland, and Arnulf Materny, Jacobs University, Bremen, Germany.


Light molecules are subject to vibration–rotation (VR) interaction, which implies corrections to the rigid rotor approximation and, in particular, corrections to spectral line intensities are related to the so-called Herman–Wallis (HW) factor. This problem is outlined here for the spectral response of some medium-weight diatomics in the gas phase and probed by means of vibrational coherent anti-Stokes Raman scattering (CARS) used for diagnostic reasons in combustion science. However, different from other works on this subject, we specialized our analysis to oxygen and, since the peculiarity of its anti-bonding molecular orbital, we find that the VR coupling is responsible for deviations that compete with the effect of Raman line widths typical of collisional environments of hot gases at room pressure. The HW correction is ultimately demonstrated to affect O2 CARS thermometry in such a manner that the accuracy for measurements at high temperatures can be improved. Copyright © 2011 John Wiley & Sons, Ltd.