Quantum-mechanical foundations of isotope chemistry

Shortly after the discovery of Isotopes Fajans ( recognized that the thermodynamic properties of solids, which depend on the frequencies of atomic and molecular vibrations, must be different for isotopes. This idea was put into quantitative form Independently by Stern ( ) and Lindemann (, )  

ACS Symposium Series American Chemical Society Washington, DC, 1975. 

Stern-Llndemann Formulation of Vapor Pressure Isotope Effect 

Equation (1) Is the first term of a Taylor expansion valid for (6/T) 2rr. For the case of the non-existence of zero point energy, one predicts an isotope effect for the Pb/ ° Pb vapor pressure ratio two orders of magnitude larger than the prediction from Eq. (1) at 600 K. In addition the no zero point energy case predicts the Pb to have the larger vapor pressure at 600 K. 

---