Physical Review A
Energy transfer by diffusion and the dipole-dipole interaction: A new perturbation expansion
Paolo Sibani, Jørgen Boiden Pedersen
Abstract
The transfer of electronic energy by diffusion and by the dipole-dipole interaction in solids and liquids is modeled by a diffusion equation with an ${r}^{\ensuremath{-}6}$ sink term plus a boundary condition at the distance of closest approach. The boundary condition is either absorptive, giving rise to diffusive transfer, or reflective, in which case the transfer is direct but modulated by diffusion. We solve the equation by a perturbation expansion in which the expansion parameter is inverse time, i.e., the $t\ensuremath{\rightarrow}\ensuremath{\infty}$ limit (the steady-state value) is reproduced exactly. The perturbation method gives accurate results for physically relevant values of the characteristic parameters and simple closed-form expressions for the time-dependent rate coefficient and the survival probability of an isolated pair are obtained for the first time when the diffusional transfer is larger than the direct transfer.