TRANSIENT PHOTORESPONSE OF THE TRIS(2,2'-BIPYRIDINE)RUTHENIUM(II)-CATALYZED MINIMAL BROMATE OSCILLATOR

The tris(2,2'-bipyridine)ruthenium(II)-catalyzed minimal bromate oscil lator under flow conditions was found to exhibit various dynamical res ponses to the pulsed-light perturbation in the visible region. The sys tem in its reduced steady state exhibits excitability with a threshold in the applied light-pulse energy, while the oxidized steady state do es not respond to the light pulse. The latter exhibits, however, a slo w response without a threshold to the negative light pulse. The system in its oscillatory state exhibits a phase shift of oscillations upon application of a pulsed-light perturbation. The oscillation phase is m ostly advanced or unaffected, depending on the phase of application of the light pulse, although a narrow region of phase delay has also bee n found in between. A phase portrait spanned by the redox potential an d the bromide ion-selective electrode potential has been determined ex perimentally on the basis of which the system dynamics is discussed in detail. All these results suggest the importance of the photoproducti on of extra HBrO2 upon pulsed-light illumination to induce the autocat alytic process that forces the system to experience a single turn alon g the limit cycle. A numerical calculation based on the Noyes-Field-Th ompson model has supported the proposed features, demonstrating that t he pulsed addition of HBrO2 reduces the concentration of Br- quickly. When it is reduced below a certain threshold value, the autocatalytic growth of HBrO2, as well as of the catalyst in its oxidized form, is i nitiated to exhibit the response corresponding to the observation.