Experiments on heavy hydrogen - V—The elementary reactions of light and heavy hydrogen. The thermal conversion of ortho-deuterium and the interaction of hydrogen and deuterium

Abstract

Since the discovery and preparation of deuterium, many of the chemical reactions of this heavy hydrogen isotope have been invalidated and compared with the corresponding reactions of ordinary hydrogen. It was soon recognized that in certain reactions the differences observed between the rate of a reaction involving hydrogen molecules and of the corresponding reaction involving deuterium molecules (D 2 ) could be explained by the assumption that the different zero-point energies of the molecules H 2 and D 2 contribute a different amount of energy for the activation process. This was, in fact, predicted by Cremer and Polanyi, and by Eyring. This difference in the zero-point energies of the initial states will cause a lower reactivity of heavy hydrogen as compared with light hydrogen. On the other hand, it was pointed out by Polanyi that the activated stats also contains a certain amount of zero-point energy which is smaller for the deuterium complex than for the hydrogen complex and that therefore the energy of activation may appear to be lowered for reactions involving heavy hydrogen when compared with the corresponding reaction of light hydrogen. The subject of the present paper is the investigation of the effect of replacing the hydrogen atoms and molecules by deuterium atoms and molecules on the rate of the interaction of hydrogen atoms and molecules according to the reaction H+H 2 ⇌H 2 +H. (1) This particular reaction involve only one reactant and a single process, and is Ike simplest chemical reaction we know. It appeared, therefore, to be an especially suitab1e example for such a study, being also well understood experimentally, and, owing to its ideal simplicity, amenable to theoretical treatment.