Anomalous Dispersion of Excitation Pulses in the 1,4−Cyclohexanedione Belousov−Zhabotinsky Reaction

The formation of stable bound wave packets is studied in a modified Belousov-Zhabotinsky reaction. These densely stacked structures arise from an attractive interaction between oxidation pulses that is not known from the classical Belousov-Zhabotinsky system. The characteristic stacking period increases with the initial concentration of bromate but decreases with cyclohexanedione. Wave stacking can also induce cascades of bunching events in which internally dense but mutually well-segregated wave clusters are formed. For different initial concentrations, the apparent merging of waves in front-to-back collisions is observed. All three modes of wave dynamics are analyzed in terms of their dispersion behavior. The dispersion relations proved to be anomalous in each case and revealed the existence of an attractor, which induces the formation of stable wave packets. The underlying mechanism has a pure reaction-diffusion character since wave propagation is not affected by fluid convection. At high initial concentrations of ferroin, complex relaxation kinetics which indicate the presence of at least two independent species that control the recovery and hence the dispersion behavior of the medium were detected. The stacking process creates either a traveling shock structure or a cascade of bunching events in which metastable wave packets are formed. The direction and the speed of the shock are explained in terms of a simple geometrical analysis. Experimental evidence for the corresponding instabilities in two-dimensional systems is presented. Here, wave stacking generates atypical structures in the collision of target patterns and wave bunching is accompanied by complex front deformations. Wave stacking and merging are also observed in thin reaction layers where they affect the evolution of target patterns. Additional results on the concentration dependences of the overall dynamics and pulse speeds are presented.