Results of thermal diffusion experiments on mixtures of gases where at least one component is a diatomic or polyatomic molecule are reported herein. The experiments were conducted in a 20-tube trennschaukel, or "swing separator," over a temperature range of several hundred degrees. Of the two mixture characteristics which influence thermal separation of the components, Delta m(ij)/mu(ij) and the intermolecular forces between components, the former was varied over a considerable range in a search for uncharacteristic behavior of the thermal diffusion factor. Three mixtures containing noble gas-nitrogen were chosen for study because of recently available theoretical calculations of the thermal diffusion factor, which included inelastic collision effects for these systems. However, anomalous behavior was observed only in the isotopic system. The effect of the molecular forces was investigated by comparing theoretical calculations of the thermal diffusion factor versus the experimental results using the best intermolecular potentials available in the literature.