ABSTRACT
I. Introduction ...................................................................................................................... 120
II. The Vapor Pressure Isotope Effect in Liquids and Solutions ......................................... 120
A. Measurements on Separated Isotopes...................................................................... 120
1. The Vapor Phase ............................................................................................... 121
2. The Condensed Phase ....................................................................................... 122
3. The VPIE........................................................................................................... 123
B. Fractionation Factors................................................................................................ 123
C. Relation of VPIE to Condensed Phase Molecular Properties
and Vibrational Dynamics ....................................................................................... 124
1. Application to Polyatomics ............................................................................... 125
2. What Happens When Molecules Condense? A Simplified
Physical Picture ................................................................................................. 125
3. VPIEs in Monatomic and Polyatomic Systems. Approximate
Vibrational Analysis.......................................................................................... 127
4. Monatomic Systems Continued. Accurate Calculations of VPIE.................... 128
5. Polyatomic Systems in First Approximation: The Cell Model........................ 129
6. Spectroscopic vs. Thermodynamic Precision ................................................... 130
7. A Further Approximation. The AB Equation................................................... 130
III. Illustrations. Representative Effects, Especially H/D Effects ......................................... 131
IV. Further Remarks on Connections with Spectroscopy ..................................................... 134
A. Anharmonicity.......................................................................................................... 134
B. The Dielectric Effect ................................................................................................ 134
1. Example, VPIE of Carbon Disulfide ................................................................ 134
V. The Molar Volume Isotope Effect ................................................................................... 136
VI. Excess Free Energies in Solutions of Isotopes. The Relation between VPIE,
the Liquid Vapor Fractionation Factor, a, and RPFR .................................................... 138
VII. Anharmonicity.................................................................................................................. 139
VIII. Some Examples ..................................................................................................................... 140
A. Ethylene.................................................................................................................... 140
B. Benzene .................................................................................................................... 141
C. Water ........................................................................................................................ 142
IX. Solute and Solvent IEs in Polymer-Polymer and Polymer Solvent Mixtures............... 145
A. Demixing of Polymer-Polymer Isotopomer Solutions .......................................... 145
B. Demixing in Polymer-Solvent Systems ................................................................. 145
X. Conclusion........................................................................................................................ 148
References..................................................................................................................................... 148
In this chapter we discuss isotope effects (IEs) on condensed phase physical properties like vapor
pressure, molar volume, compressibility, expansivity, heats of vaporization or solution, and so
forth, for liquids, solids and solutions. Some properties (for example the vapor pressure isotope
effect or VPIE) are of great practical interest because they form the basis for isotope separation
(e.g., distillation, solvent extraction, etc.).
