The Relative Reaction Velocities of Isotopic Molecules

Abstract

The rate constants for competitive reactions of isotopic molecules are considered from the theory of ``absolute rates'' and the collision theory. Formulas are derived for the ratio of the rate constants and the difference in the activation energies for reactions of isotopic molecules. The difficulties in the a priori calculation of relative rates are pointed out and discussed. In general the rate constant for the light molecule will be greater than that of the heavy molecule. It is shown that the maximum ratio in the rates occurs when the isotopic atom is essentially free in the activated complex. The conditions for the rate constant of the heavy molecule to exceed that of the light one are formulated. It is shown that the difference in activation energies covers the range from zero to the difference in the differences in the zero‐point energies of the reacting molecules and their respective activated complexes.