title: The Methyl-Rotor Electron-Spin Dynamics in the Smoluchowski Drift-Diffusional Framework
abstract: The EPR behavior of the internal motion of the methyl fragment in radicals is simulated using the Smoluchowski drift diffusion model. EPR stochastic Liouville lineshape calculations using this model are presented, allowing the exploration of the whole span of conditions between the discrete-site-exchange and the stepless-free-diffusion limits and offering a unification of these two approximate theories. An accurate value of the correlation time for the isotropic hyperfine interaction is calculated for the full ranges of the parameters describing the system and is compared to those given by the approximate models in the two limiting cases, allowing for a discussion of their quality. Long and short correlation time limit spectra are reported and interpreted using analytic models. For the isotropic hyperfine interaction studied here, no broadening effects are observed under Redfield (strong narrowing) conditions. This suggests absence of lifetime broadening effects in agreement with site-model results. The addition of a cos varphi term in the hyperfine interaction is essential for pyramidal radical centres, as is demonstrated by simulation of experimental reports in the literature.
authors.affiliation: Department of Physics, University of Oslo, Oslo, N-0316, Norway
authors.initials: AR
authors.lastname: S&Oslash;rnes
authors.initials: NP
authors.lastname: Benetis