The backward stochastic Liouville equation is formulated in a Dirac-type notation in order to emphasize the kinship with the backward diffusion equation and the Heisenberg picture of quantum mechanics. The backward equations are useful both for analytic treatments and for numerical methods since the solution contains the average value of the observable for all initial spin and spatial conditions. The crucial point in using the backward equations is the boundary and initial conditions, which are derived for an arbitrary observable A and corresponding rate of change A. The formalism is applied to derive explicit analytic expressions for the recombination yield of two radicals that performs a free diffusion in a liquid under high magnetic fields. It is shown that the nontrivial. limit of diffusion-controlled. reaction can be directly calculated by a careful choice of boundary conditions.