Thermal Conductivities of Gaseous H₂O, D₂O, and the Equimolar H₂O—D₂O Mixture

Measurements have been carried out over the temperature range 380°—525°K using a four‐cell hot‐wire thermal‐conductivity apparatus. At the lower temperatures the thermal conductivities of H₂O and D₂O are identical, but at the highest temperature the conductivity of D₂O is larger by 8–9 parts per thousand. Conductivities of the equimolar mixtures lie midway between the conductivities of the pure components. Results are analyzed to test a recent hypothesis that a resonant exchange of rotational quanta causes the thermal conductivity of a polar gas to seem anomalously low in relation to its viscosity. It is concluded that the interchange of rotational energy between neighboring dipoles may be important, but that exact resonance is probably not required, at least in the case of water vapor.