The carbon and oxygen isotope fractionation factors in the liquid–vapor equilibrium (LVIFF) of carbon monoxide have been determined over the temperature range 81–125° K. The results are in excellent agreement with previous isotopic vapor pressure data which cover the range 68–82° K. The results are analyzed in terms of an anharmonic cell model by the FG matrix method. The anharmonicity is approximated by the use of a temperature dependent F matrix. Analysis of the LVIFF and VPIE data by this method gives good agreement with experiment and the previous theoretical calculation by Gordon of the mean square force, the mean square torque, and the translation rotation coupling at 77.5° K. The present calculations of the mean square force and experimented data on the mean energy in liquid CO are used to derive a set of intermolecular potential parameters for CO using the WCA perturbation theory. If a m-6 potential is assumed, the best fit of all the data is obtained for m=14, ε/k=109° K, and σ=3.858Å. The latter are consistent with potential parameters derived from second virial coefficients and gas viscosity.
The fractionation of the oxygen isotopes in solutions of LiCl, NaCl. KCl, KBr, KJ and CsCl with H2O and D2O as solvent has been measured at 25 °C by means of the CO2-equilibration technique. As opposed to earlier measurements a slight anion dependence for the potassium halides has been found in H2O. This anion effect is much more pronounced in D2O. It even leads to a change in the directions of the 180 enrichment between cationic hydration water and bulk water for KCl and KBr. The absolute values of the fractionation factors for LiCl and CsCl, which differ in sign in H2O in agreement with positive and negative cationic hydration, respectively, as known from other kinds of measurements, is increased for LiCl and decreased for CsCl in D2O. There is no fractionation of the oxygen isotopes between hydration water and bulk water in both solvents for NaCl.
The solvent isotope effect is explained by the stronger anion influence on the structure of the bulk water in D2O as compared with H2O. This stronger influence is expected because of the higher structural order in D2O than in H2O at the same temperature.
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