C. Gardner Swain

The nature of the structure difference between light and heavy water and the origin of the solvent isotope effect—I

Abstract The observed differences in heat content, entropy and free energy of light and heavy liquid water can be calculated within experimental error from measured infrared frequencies, using a model for water with tetrahedral hydrogen bonding and treating the hindered rotations (librations) of the water molecules as three-dimensional isotropic harmonic oscillators. The origin of the solvent isotope effect for monatomic ions in light and heavy water is their effect on the structure difference between light and heavy water. The quantity Δθ = h Δν/k provides a measure of this structure difference, where Δν is ν−ν′, the difference in average values of the librational frequencies of H2O and D2O, and ν′=ν/1·3815. Differences in heat content, entropy and free energy for solution of monatomic ions in light and heavy water and individual ionic activity coefficients can be calculated from Δθ. Hydronium and hydroxide ions are also discussed.

A theoretical interpretation of isotope effects in mixtures of light and heavy water—II

Abstract Solvent isotope effects for H 2 OD 2 O mixtures and for ionic hydration equilibria in such mixtures can be calculated from the structure difference between D 2 O and H 2 O and that between HDO and H 2 O and the relative amounts of the three waters. The behavior of acids in H 2 OD 2 O mixtures is considered in detail. Dissociation constants of acetic acid are calculated over the complete range of deuterium concentrations and found to agree with the experimentally determined ones. The Gross equation for the dependence of isotope effect on mole fraction of deuterium for acid-catalyzed reaction of substrates S proceeding via SL + transition states (LH or D) is derived from first principles.