Abstract
The anisotropic components of Raman vibrational Q-branch transitions are theoretically predicted to have larger collisional linewidths than those of the isotropic components, owing to broadening contributions by collisions that reorient the molecular angular momentum. We report experimental observations of this effect for linewidths of the isotropic and anisotropic components of H2Q-branch transitions, measured at 296 K using high-resolution coherent anti-Stokes Raman spectroscopy. Differences in these linewidths are a direct measure of state-resolved reorientational broadening and are in good agreement with theoretical predictions and with related experimental results. The Galatry soft-collision line-shape model yields excellent fits to the anisotropic and isotropic line shapes but exhibits a slight density dependence in the best-fit motional narrowing coefficients at low densities. No difference is observed between the narrowing coefficients for isotropic and anisotropic spectra. Also, by comparing our measurements of rovibrational O-branch linewidths with measurements of pure rotational S-branch linewidths by Keijser et al. [Physica 76, 585 (1974)], we obtain estimates of broadening by elastic vibrational dephasing.
© 1989 Optical Society of America
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