QUENCHING OF OSCILLATIONS IN THE PERMANGANATE-HYDROXYLAMINE REACTION

Perturbation experiments on small-amplitude oscillations of the MnO4--NH2OH-H3PO4 system are reported. We show that the oscillations arise from a stable stationary state by a supercritical (i.e. continuous) Hopf bifurcation, and demonstrate that the oscillations can be quenched (temporarily stopped) by addition of small amounts of either of the species Mn2+, OH-, or colloidal MnO2 at specific phases. Characteristic times exceeding two hours are observed for the return to the limit cycle oscillations from successful quenchings. Remarkably, this is more than 40 times the residence time of the flow system. The work is the first part of a study aiming at developing a model of the complicated permanganate oscillator, including a determination of the rate constants of the reactions taking place.