Stochastic modeling of partially diffusion-controlled reactions in spur kinetics

Abstract

Stochastic simulation techniques have been developed for modeling partially diffusion-controlled reactions in spur kinetics. These methods have been used to examine whether deviation from full diffusion control influences the overall spur chemistry.Studies of idealized two-species spurs suggest that the time dependence of the kinetics is not affected by the nature of the reaction; however, the overall chemistry of a spur can be influenced by a deviation from full diffusion control as whether the reaction is fully or merely partially diffusion controlled can have a sisnificant effect on the initial overlap of the reactants. The reaction at time zero, which depletes the yield of reactants, is determined by the relative values of the width of the spur and of the encounter radius. This depletion is of particular importance in the radiation chemistry of water where the spatial distribution of the hydroxyl radical in a spur is believed to be significantly tighter than the distribution of the hydrated electron.

Monte Carlo simulation of physicochemical processes of liquid water radiolysis

“…A value of 0.5 nm was chosen for a, then the reaction velocity v was estimated by [33] (33) k D a a D = ′ + ′ In IRT simulation, for the realization of a system of n p particles, it is necessary to consider n p (n p -1)/2 reaction times by Eq. (36). When modeling scavenger reactions, it is also necessary to include n s OH scavenger particles, and consider the reaction OH + scavenger → removal of OH (38) The total number of the combination was too large to handle even at dilute scavenger concentrations, so we treated the scavenger as a continuum, then each radical was initially surrounded by a homogeneous distribution of scavengers.…”

“…The random reaction time T r was determined by solving Eq. (25) as (36) where ξ is a random number uniformly distributed between 0 and 1 and erfc -1 (x′) = x is the inverse of erfc (x) = x′ [33]. The probability of the reaction is largest when T r is the smallest.…”

“…(37). When two radicals are created in the reaction, the coordinates of products were determined using reflecting boundary conditions [36]. …”

Independent reaction times method in Geant4‐DNA: Implementation and performance

“…55 Nevertheless, it has been shown that the yields calculated with SBS are equivalent to IRT when using two-particle systems. 3,24,56 In addition, the G-values calculated with the SBS approach depended to some extent on the minimum time step which is implemented in a dynamic time partition. 19 To quantify this effect, we calculated G-values for • OH produced by 1 MeV electrons using a fixed minimum time step to 0.1 ps.…”

“…The differences might be attributed in part to the independent pair approximation taken by the IRT approach whereas the SBS considers a multiparticle system 55 . Nevertheless, it has been shown that the yields calculated with SBS are equivalent to IRT when using two‐particle systems 3,24,56 . In addition, the G‐values calculated with the SBS approach depended to some extent on the minimum time step which is implemented in a dynamic time partition 19 .…”