Generalized wigner law in a static electric field

We derive a general expression for the photodetachment transition rate from a negative ion with the excess electron bound in a definite angular momentum state, both with and without an applied field. The field-free case is shown to reduce to the standard Wigner law. With a non-zero field the situation is more complicated; unlike in the simple Wigner law, the transition must be described not only by the electron's final angular momentum but by its initial angular momentum as well. This is a direct result of the breaking of the ion's spherical symmetry by the field. Detachment below threshold and oscillatory structure above threshold are predicted for all ell ' to ell transitions. This general model is consistent with previous calculations of certain specific cases