A considerable amount of work has recently been done on the application of wave-mechanics to the theoretical study of chemical reactions. This has consisted chiefly in calculating activation energies and strengths of various bonds by consideration of electronic states in molecules. Some work has also been done on actual reaction mechanisms. It is evident from the latter that, owing to the large masses of the particles concerned, the quantum theory and the classical treatment will give different results only for reactions involving hydrogen or diplogen. Previous attempts to deal with such reactions have consisted simply of calculating the permeability G(W) of a barrier of height equal to the activation energy for protons of energy W. The reaction rate is then assumed to be given by