Thermal diffusion of Br2 and Cl2 in the noble gases

We have measured the thermal diffusion factors of Br2 and Cl2 in He, Ne, Ar, and Kr. The halogen-noble gas mixture is contained in a closed two bulb apparatus, the ends of which are maintained at different temperatures. The halogen density at the cold end is determined by the equilibrium vapor pressure above the temperature controlled halogen reservoir. The halogen density at the hot end is determined by measuring the total reaction rate; γ of sodium atoms with halogen molecules. Since the cross sections for the reactions of Na atoms with Br2 and Cl2 are known, measurement of γ yields directly the halogen density. The thermal diffusion factors computed from the transport equations are compared with the first Kihara approximation to the Chapman-Enskog theory. The agreement is within experimental error.