Viscosity of the Isotopes of Hydrogen and their Intermolecular Force Potentials

Abstract

Measured values of the viscosity are presented for the three isotopes of hydrogen: H₂, HD, and D₂ at 20°C and at 30°C, all under atmospheric pressure. The ratios of the viscosity of any one pair of the above gases is obtained very accurately, the major source of error being connected with the uncertainties in the knowledge of the impurities present in the gases. On the basis of the Chapman‐Enskog theory for the viscosity of gases composed of spherically‐symmetrical molecules whose potentials can be represented by the product V(r) = εf(σ/r), it is concluded that all three isotopes have different intermolecular constants. However, the differences which characterize the intermolecular potentials of H₂ and D₂ are not likely to be large. Calculations which attempt to take into account the differences in the potentials of H₂ and D₂ by differences in polarizability are not confirmed by the present measurements.