Probability of Exit Boundary Neutral Species

To calculate the probability of moving up or down a slice for a diffusion process one needs to solve the backward diffusion equation subject to the boundary conditions p B ) = 1 and p(A ) = 0 (i.e. the distance of the radical pair moves one slice further apart). The complete derivation is presented in Sect. A.3 of the Appendix, with the final exit probability found to be 

Similarly, using the boundary condition p A ) = 1 and p B ) = 0 (the probability of moving down one sUce) is given as 

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