Hydrogen-deuterium exchange reaction experimental data

The great majority of experimental data (see Section III.A) indicate that the hydrogen-deuterium exchange reaction belongs to the class of acceptor reactions (i.e., reactions that are accelerated by electrons and decelerated by holes). This means that the experimenter, as a rule, remains on the acceptor branch of the thick curve in Fig. 8a, on which the chemisorbed hydrogen and deuterium atoms act as donors. Here a donor impurity must enhance the catalytic activity, while an acceptor impurity must decrease it. This is what actually occurs, as we have already seen (see Section III.A). 

It was found from the o — M —O + Hj O M o experimental data that all metals that can chemisorb hydrogen can catalyze hydrogen-deuterium exchange reaction. The results provide a powerful evidence for dissociation adsorption of hydrogen. 

The pressure P is contained in formula (62) not only in an explicit form but also in terms of the parameters e8 and e8+, as seen from (5), because s and e8+ are, generally speaking, functions of pressure. In our model, however, 8- and e8+ may be regarded as independent of P since the surface is supposed to be saturated with hydrogen and deuterium atoms (all the adsorption centers are assumed to be occupied). Thus, the hydrogen-deuterium exchange proves, in accordance with (63), to be a reaction of the first order with respect to hydrogen (deuterium), which is consistent with numerous experimental data (see Section III.A). 

In the simplest cases, the reactant and the transition state will have only one and the same exchangeable position for hydrogen or deuterium. In such cases, the shape of the curve obtained from Eq. (17.72) provides a way of calculating the fractionation factors in the reactant and the transition state of reaction, directly from the experimental data (Candour Schowen, 1978). 

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