Study of the Extinction Dynamics of the Mercury Beating Heart Reaction in Acid Solution and in the Presence of γ-Radiation

Abstract

The dynamics of the oscillatory mercury beating heart (MBH) reaction in acid aqueous solution with CeIV as the oxidizing agent was investigated. The reaction slowly runs down over a period of a few hours, until all oscillatory activity eventually ceases. During this period the dynamics slowly evolves, showing qualitatively different forms of oscillations. These oscillations display different modes of oscillations with geometric structures similar 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 appear successively. However, these oscillations are damped and could be interpreted in terms of a subcritical Hopf bifurcation. We propose different oxidation−reduction reactions to explain the appearance of these cycles based on the formation of mercury(I) species, in the form of free Hg22+ 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 without adding the CeIV oxidant, generating in situ species of Hg(I) by γ-irradiating the metallic Hg in the same acid solution as before. It is shown that 60Co γ-rays induce the generation of oscillations. In this way we support our claim that oscillations are due to the formation of chemical species of Hg(I) be it ionic or molecular and that extinction occurs when [Hg(II)] ≫ [Hg(I)].