Velocity dependence of fine-structure changing collisions of Na with Ne, Ar, Kr, Xe, N₂and CO₂

The authors present measurements of the velocity dependence and absolute magnitude of the fine-structure changing collision cross section for Na(3p) in collisions with Ne, Ar, Kr, Xe, N 2 and CO 2 . The measurements were made in a gas cell using a technique based on the Doppler shift to achieve the velocity selection. The validity of the technique is established both by careful study of possible systematic effects and by comparison with recent crossed beams measurements where available. The results for rare-gas targets are compared with both semiclassical and quantal calculations; those by Pascale and Olson given excellent agreement for Ar, good for Xe (the calculated magnitude is too big), and fair for Ne and Kr (both magnitude and velocity dependence are somewhat outside error). The N 2 results agree with the magnitude of recent calculations. The CO 2 results are anomalously small at low relative velocity; this is attributed to competition from quenching processes.