Study of the extinction dynamics of the mercury beating heart reaction in acid solution and in the presence of gamma-radiation

The dynamics of the oscillatory mercury beating heart (MBH) reaction in aci d aqueous solution with Ce-IV as the oxidizing agent was investigated. The reaction slowly runs down over a period of a few hours, until all oscillato ry activity eventually ceases. During this period the dynamics slowly evolv es, showing qualitatively different forms of oscillations. These oscillatio ns display different modes of oscillations with geometric structures simila r to heart, circle, pentagon, hexagon, and 8- and 16-pointed stars. As time proceeds, limit-cycle oscillations of period-1, period-3, and period-2 app ear successively. However, these oscillations are damped and could be inter preted in terms of a subcritical Hopf bifurcation. We propose different oxi dation-reduction reactions to explain the appearance of these cycles based on the formation of mercury(I) species, in the form of free Hg-2(2+) ion or , in molecular form, as a soluble mercurous sulfate or a mercurous sulfate film. The theoretical potential values calculated for these reactions agree well with our experimental values. An experiment was performed also withou t adding the Ce-IV oxidant, generating in situ species of Hg(I) by gamma -i rradiating the metallic Hg in the same acid solution as before. It is shown that (CO)-C-60 gamma -rays induce the generation of oscillations. In this way we support our claim that oscillations are due to the formation of chem ical species of Hg(I) be it ionic or molecular and that extinction occurs w hen [Hg(I)].