SCALING BEHAVIOR OF DIFFUSION-LIMITED ANNIHILATION REACTIONS ON RANDOM-MEDIA

We investigate numerically the kinetics of diffusion limited annihilat ion reactions in disordered binary square lattices where the reacting particles are constrained to diffuse on a concentration of the lattice sites. We find that the asymptotic decay of the particle concentratio n in the percolative regime is of the form c(t,p)-c(r)(p) alpha t(-ds/ 2), where c(r)(p) is the concentration of residual particles. We recov er well known results such as d(s)(p>p(c))=d=2 with logarithmic correc tions, and d(s)(p(c))=1.34+/-0.02. For p<p(c) we employ a scaling theo ry and collapse the data onto a universal form dc/dt=tau(-(ds(pc)/2+1) )f(t/tau), With tau being a characteristic diffusion time and f(t/tau) representing the crossover from a power law decay to a stretched expo nential one. We relate the present results with the kinetics of the ex citation reaction (triplet + triplet -> singlet) on isotopic mixed cry stals of naphthalene. (C) 1996 American Institute of Physics.