Near-infrared sub-Doppler saturation recovery kinetics of CN radicals will be reported, illustrating a clear signature of speed-dependent rates for rotational energy transfer. Related effects are commonly invoked in the interpretation of pressure-broadened line shapes beyond the Voigt approximation, in a regime where physically distinct mechanisms of velocity-changing collisions (Dicke narrowing) and velocity-dependent collision rates can produce qualitatively similar deviations from Voigt lineshapes. Pressure-dependent recovery rates of CN transient absorption, following either broad-band bleaching or sub-Doppler bleaching are found to be remarkably similar. Velocity-changing collisions thus appear to make a minor or negligible contribution to the rate of sub-Doppler depletion recovery. The velocity-resolved kinetic studies are applied to the interpretation of pressure-dependent broadening and shifting of CN A-X lines by argon, also performed in our laboratory. Detailed comparison with quantum scattering calculations will be possible.

Speed-dependent collision rates in rotational energy transfer and pressure broadening

245th National Meeting (2013)

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