The influence of the distribution of atomic masses within the molecule on thermal diffusion: I. Isotopic CO and N 2 molecules

Abstract

Separations by thermal diffusion in different isotopic mixtures of CO and N 2 were studied in a “Trennschaukel” between 80°K and 303°K. The observed separations were strongly influenced by the distribution of the atomic masses within the molecule. For the mixtures 12C 18O/ 12C 16O, 14C 16O/ 12C 16O and 12C 18O/ 14C 16O the thermal diffusion factor becomes zero at 110°K, 175°K and 250°K respectively. These differences cause very big differences in experimentally established potential parameters. The separations are very well described by the dimensional treatment of Waldmann which gives the thermal diffusion factor as a sum of a translational and a rotational part. From the observed separations the dependence of the diffusionconstant on temperature was calculated. Within the usual experimental accuracy no difference is found between the different isotopic molecules.