“…What is referred to here is the principle that the exchange of energy accompanying these reactions is not primarily a mechanical problem of collisions, but that the efficiency of the energy transfer will depend upon the strength of the interactions of the electronic fields of the colliding species. The use of potential-energy curves, which take this electronic interaction into account explicitly, is, however, more than just a more elaborate formulation; their use offers one of the most practical quantitative approaches to the general problem of energy interchange (and chemical reactions) whose basic qualitative formulation was laid down by Franck and Eucken. Potential-energy surfaces have proved useful not only in discussing the mechanism of reactions involving electronically excited species, but also in an understanding of the specific magnitudes of quenching cross-sections (102,141,206) (see Section III B). Potentialenergy surfaces have also been utilized in discussing the interconversion of translational and vibrational energies (18,33,61,88), and further progress in the general field of energy interchange in inelastic collisons, a problem intimately connected xvith the mechanisms of reactions, may well be made by a study of the pertinent potential surfaces in the manner outlined above.…”