Spin Effects on Spur Kinetics. 5. Modeling of Coherent Phenomena

We report an extension to our modified Monte Carlo simulation technique to model coherent spin effects (such as CIDEP) in spurs containing one or two pairs of neutral radicals under the influence of an applied magnetic field. The motivation for choosing such a system is to investigate whether it is possible to glean information about the initial distribution of the particles or the initial spin state of the spur from the simulated polarizations. An analysis of the system based upon the adiabatic approximation provides qualitative insight. However, further examination indicates that while it is possible to obtain explicit information about the initial spin state from the polarizations, the same does not appear to be true for the spatial configuration. The results for a two-pair spur are very different from those obtained for a single pair. To determine whether the two-pair polarizations can be explained in terms of pairwise interactions, and to mask the effects of averaging inherent in Monte Carlo simulations, single realizations of the spur evolution were performed. These indicate that at short times (<100 ps) the polarizations are induced in a complicated manner through the close proximity of all four particles, while at longer times successive two-body encounters are responsible.