The long time behavior of initially separated A + B → 0 reaction - diffusion systems with arbitrary diffusion constants

We examine the long time behaviour of A + B → 0 reaction diffusion systems with initially segregated species A and B. All of our analysis is carried out for arbitrary (positive) values of the diffusion constants DA, DB, and initial concentrations a0 and b0 of A’s and B’s. We divide the domain of the partial differential equations describing the problem into several regions in which they can be reduced to simpler, solvable equations, and we merge the solutions. Thus we derive general formulae for the concentration profiles outside the reaction zone, the location of the reaction zone center, and the total reaction rate. An asymptotic condition for the reaction front to be stationary is also derived. The properties of the reaction layer are studied in the mean-field approximation, and we show that not only the scaling exponents, but also the scaling functions are independent of DA, DB, a0 and b0.