Velocity Dependence of Na-Ar and Na-Xe Fine-Structure-Changing Collisions

The velocity dependence of the total fine-structure-changing cross section has been measured for collisions of Na(3p) with Ar and Xe using a new velocity-selection technique based on the Doppler shift. The velocity dependence agrees with recent theoretical predictions of Pascale and Olson, but the magnitudes of the cross sections do not.