Diffusion coefficients of isotopic mixtures of CO and N 2

Abstract

Relative diffusion coefficients as a function of temperature have been determined for the systems 12C 18O- 12C 16O, 13C 16O- 12C 16O, 12C 18O-N 2, 13C 16O-N 2 and 14N 15N- 14N 2. The measurements have been performed in the temperature range from 230 K through 425 K. The method which has been used gives an accuracy in the values of the diffusion coefficients of 0.1%, relative to those at room temperature. By normalizing to argon, absolute values for the different mixtures could be obtained. Above 300 K the behaviour of the diffusion coefficients as a function of temperature could be described with the monatomic gas theory, yielding ϵ/ k values in the order of 80 K. A mutual comparison between the values for the different mixtures, however, is inconsistent with a monatomic description. Below 300 K the temperature dependence for all mixtures strongly deviates from a monatomic behaviour. The results are discussed in connection with thermal diffusion.