Nonclassical kinetics of an elementary A+B-->C reaction-diffusion system showing effects of a speckled initial...

We demonstrate here the implementation of an experimental system suitable for the study of the diffusion limited A+B-->0, nonclassical reaction behavior. Using a combination of a fluorescent calcium indicator and a calcium ion which is initially "caged," a pulse of near-UV light initiates the reaction which is followed as product formation vs time. Sensitive dependence on the initial reactant distribution is observed through patterns in the uncaging UV light profile. In one case, the reaction progress passes through two nonclassical time regimes, one due to roughness originating from laser speckles, followed by one consistent with the three-dimensional Zeldovich rate of (1/rho(A)-1/rho(A0)) approximately t(3/4), with features matching Monte Carlo simulations on this initial distribution. This behavior is contrasted with reactions initiated by a homogeneous source which induces random initial reactant distributions, though both systems seem to approach the asymptotic limit of self-segregation of reactants.