Laboratory studies of gas phase sodium diffusion

The gas phase diffusion coefficients of Na in Ne, N2, and CO2 were measured in a flow tube with an oven source and resonant fluoresence detection of Na. DNa,Ne=209±21 cm2 Torr s−1 at 281 K, DNa,N2=129±13 cm2 Torr s−1 at 281 K, and DNa,CO2=134±13 cm2 Torr s−1 at 281 K. DNa,He was measured over the temperature range 211– 424 K. DNa,He(T)=(385±40) (T/300)(1.72±0.18) cm2 Torr s−1. The experimental results are compared with previous studies. The sticking coefficient for Na on the walls of the flow tube was determined to be approximately equal to 1 by an analysis of the diffusion coefficient data. The results for DNa,He, DNa,Ne, and DNa,Ar are compared with the predictions of Chapman–Enskog calculations using Na–noble gas potentials from recent spectroscopic measurements.