Regular and Irregular Spatial Patterns in an Immobilized-Catalyst Belousov-Zhabotinsky Reaction

FKN mechanism of the BZ reaction (expanded “Oregonator”) agree surprisingly well with the experimental data. Similar conclusions hold in the case when the system of two coupled CSTR’s with forcing of one of them is inve~t iga ted .~~ Both permanent and temporal extinction of oscillations are observed and m ~ d e l e d . ~ ~ . ~ ~ Early experimental observations of complex chemical wave trains generated by periodic perturbations are due to Showalter, Noyes, and Turner.22 They used the BZ reaction on a Petri dish periodically perturbed by voltage pulses on a Pt-Ag electrode couple. Farey ordering of periodic wave trains and a devil’sstaircase-like structure in a similar experimental system were reported in ref 25. We consider the narrow tube used here to be a more controllable experimental system than the Petri dish. It is satisfactory that the results of the experiments reported here agree well with those published p rev io~s ly .~~ When periodically forced, both oscillatory and excitable BZ systems reveal striking similarities in the arrangement of resonance regions and in parameter dependences of the firing number. Despite the lack of any apparent periodicity in the unperturbed excitable system, a “latent” periodicity is excited by the forcing. The difference between such a “latent” periodicity and a true one is reflected in the fact that the firing number ranges only from 0 to 1 in the forced excitable system while it may take on an arbitrary value in the forced oscillatory system. There seems to exist already a solid basis of experimental studies on periodic perturbations of chemical oscillations; cf. papers by Rehmus and Ross in ref 2 and the paper by S ~ h n e i d e r ~ ~ for a review. We believe that a similar basis should be built for chemical excitable systems. Registry No. BrO,-, 15541-45-4; malonic acid, 141-82-2; ferroin, 14708-99-7.