Computer Simulation of Diffusion-Limited Chemical Reactions in Three Dimensions

Rates of transient diffusion-limited chem ical reactions in three dimensions are de termined by Monte Carlo computer simu lation. Particles are initially placed at random on a cubic periodic Euclidean lat tice and perform independent random walks. Pairs of particles arriving at the same site are reacted according to the rules of particular types of chemical reac tion; annihilation, bimolecular, and cata lytic reactions are simulated. The compu tational method involves searching par tially ordered lists of the particles' coordinates, to find any particles sharing a lattice site. We observe the effects of the diffusion coefficients and the stoichi ometry of the reactive species on the rate of reaction. The results strongly support the contention that the Smoluchowski- Noyes theory does not give a uniformly accurate prediction of diffusion-limited re action rates in three dimensions. The only case of substantial disagreement between the simulation results and the theory is found for nearly equimolar bimolecular reaction.