Pressure and temperature effects on the excess deuteron and proton conductance

Abstract

The limiting molar conductances Λ° of deuterium chloride DCl in D2O were determined as a function of pressure and temperature in order to examine the proton-jump mechanism in detail. The excess deuteron conductances λ°E(D +), as estimated by the equation [λ°E(D +) = Λ°(DCl/D 2 O) − Λ°(KCl/D 2 O)], increases with an increase in the pressure and temperature as well as the excess proton conductance [λ°E(H +) = Λ°(HCl/H 2 O) − Λ°(KCl/H 2 O)]. The isotope effect on the excess conductances, however, depends on the pressure and temperature contrary to the model proposed by Conway et al.: λ°E(H +)/λ°E(D +) decreases with increasing pressure and temperature. The magnitude of the decrease with pressure becomes more prominent at lower temperature. These results are discussed in terms of the pre-rotation of adjacent water molecules, the bending of hydrogen bonds with pressure, and the difference in strength of hydrogen bonds between D2O and H2O.