INFLUENCE OF HEAVY-WATER ON THE BRAY-LIEBHAFSKY OSCILLATING REACTION

The influence of heavy water on the Bray-Liebhafsky (BL) oscillating r eaction was investigated for varying amounts of D2O, at three differen t temperatures. Evolution of the system was monitored potentiometrical ly. Simultaneous recordings of gaseous oxygen over the reaction soluti on were also performed. In separate experiments the iodine concentrati on was monitored spectrophotometrically. Replacement of H2O by D2O pro gressively intensifies the reactions of oxidation of the iodine specie s, compared to the reactions of their reduction. As a result there is a critical ratio of D2O/H2O, after which the dynamics of the system is considerably altered. The same effect is observed at all temperatures , but it is more pronounced at lower temperatures. Two possible explan ations for the progressively intensified oxidation are discussed: the reverse isotope effect and the selective energy transfer. It is establ ished that the oxidation and reduction of the iodine species in the BL reaction do not proceed through the same intermediates. The important role of bulk water in surmounting the high activation energy threshol d of the oxidation branch is revealed in the experiments.