INVESTIGATION OF A MONTE-CARLO MODEL FOR CHEMICAL-REACTIONS

Monte Carlo computer simulations are in use at a number of laboratorie s for calculating time-dependent yields, which can be compared with ex periments in the radiolysis of water. We report here on calculations t o investigate the validity and consistency of the procedures used for simulating chemical reactions in our code, RADLYS. Model calculations were performed of the rate constants themselves. The rates thus determ ined showed an expected rapid decline over the first few hundred ps an d a very gradual decline thereafter out to the termination of the calc ulations at 4.5 ns. Results are reported for different initial concent rations and numbers of reactive species. Generally, the calculated rat e constants are smallest when the initial concentrations of the reacta nts are largest. It is found that inhomogeneities that quickly develop in the initial random spatial distribution of reactants persist in ti me as a result of subsequent chemical reactions, and thus conditions m ay poorly approximate those assumed from diffusion theory. We also inv estigated the reaction of a single species of one type placed among a large number of randomly distributed species of another type with whic h it could react. The distribution of survival times of the single spe cies was calculated by using three different combinations of the diffu sion constants for the two species, as is sometimes discussed in diffu sion theory. The three methods gave virtually identical results.