Molecular Diffusion Studies in Gases at High Temperature. IV. Results and Interpretation of the CO2–O2, CH4–O2, H2–O2, CO–O2, and H2O–O2 Systems

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Abstract
Experimental measurements of the binary diffusion coefficients for the CO2–O2, CH4–O2, H2–O2, CO–O2, and H2O–O2 systems over the nominal temperature range 300–1000° K are reported. The measurements were made by the point source technique. The data have been analyzed in terms of intermolecular potential energies and the rigorous kinetic theory by using the Lennard‐Jones (12–6), modified Buckingham (Exp‐6), point center of repulsion (inverse power), and the exponential repulsion potential energy functions. It is shown that all four of these functions are capable of fitting the diffusion data with about the same precision (within experimental error). However, the potential energy values themselves which are calculated from these four different fitted models are shown to be widely at variance; especially in the range of interaction corresponding to the lower temperatures. Thus, these results provide an example of the high degree of ambiguity (previously noted by several others) involved in deducing intermolecular potential energies from transport data. The use of such fitted potentials to extrapolate transport data to higher temperatures, on the other hand, is probably a more reliable procedure, and diffusion coefficients for the above five gas pairs (in their unexcited, undissociated states) have been estimated to 3000° K from the potentials based on the 300–1000° K measurements.