ORIGIN OF CHEMICAL-INSTABILITY IN THE BROMATE-SULFITE FLOW SYSTEM

The origin of the instability observed in the bromate-sulfite-proton s ystem is discussed. This is known as the subsystem of some pH oscillat ors which provides the positive feedback channel for H+. It is compose d of the following two fast equilibria: H+ + SO32- <-> HSO3- and H+ HSO3- <-> H2SO3 and the oxidation of HSO3- and H2SO3 by BrO3- to recov er the initially supplied proton as 3HSO(3-) + BrO3- --> 3SO(4)(2-) Br- + 3H(+) and 3H(2)SO(3) + BrO3- --> 3SO(4)(2-) + Br- + 6H(+). This scheme exhibits bistability under flow conditions. It gives rise to ch emical oscillations if it is coupled with a simple linear decay proces s of H+ as a negative feedback channel. It is also capable of exhibiti ng chaotic behavior in the presence of HCO3-. We analyze the nature of the strong nonlinearity provided by the above scheme in detail and sh ow that it arises essentially from the fast reaction of H2SO3 with bro mate. The simplicity of the scheme enables us to describe the system d ynamics with three variables without any approximation. As a result, w e now have a model in hand in which we can compare the theoretical res ults directly and quantitatively with the corresponding experiments. T his situation may open a way to understand the complexity in nonlinear chemical systems in a more quantitative manner. Some recent experimen tal findings of complex oscillatory behavior including chaos for the s ystem with more realistic negative feedback channels, or for the syste m in which BrO3- is replaced with H2O2, are discussed on the basis of the present analysis. (C) 1996 American Institute of Physics.