Electron-ion geminate escape probability in anisotropic media

The diffusion-controlled electron-hole geminate escape probability in anisotropic media has been calculated by numerical solution of the adjoint equation for that probability after a series of simplifying transformations. Relative to the crystalline axes the anisotropies of both dielectric constant and mobility, which generally have different principal directions, are important. The escape probability depends on the magnitude and direction of the initial electron-hole separation. Applied to anthracene the implied experimental escape probability ≈0.01 is attained at initial separations 4.0, 4.0 and 3.2 nm along the a, b, c′ crystal directions respectively.