Reaction Rates of the Hydrogen Isotopes

Abstract

IT seems to be generally assumed that diplogen will always react more slowly than hydrogen. As I may partly be responsible for this view¹, I should like to point out that this is not always correct. Lower reactivity of diplogen compared with hydrogen results mainly from two causes: (1) the existence of zero point energy: and (2) the quantum mechanical leakage of particles through energy barriers. Whilst the leakage through the barrier is always greater for the hydrogen than for the diplogen atoms, the effect of the zero point energy may occasionally favour the reverse ratio. I will confine myself to one special case, as the general treatment will be published shortly by C. E. H. Bawn and G. Ogden. Compare the reaction of a free hydrogen and a diplogen atom ; in the initial state the atoms possess no zero point energy and their energies will be equal. However, at the top of the barrier there will be a zero point energy present², and this will be greater for the complex reacting with the hydrogen atom than for that reacting with the diplogen atom. The effect of the zero point energy at the top of the barrier is, therefore, to increase the activation energy of the hydrogen atoms to a greater extent than that of the diplogen atoms.