Green-function approach to electron angular correlations in the Wannier threshold law

The angular distribution of electrons near the threshold of double ionization is considered in the framework of the Wannier mechanism [Phys. Rev. 90, 817 (1953)]. The wave propagation from the reaction to the free zone along the Wannier saddle is calculated in a general form for an arbitrary initial condition. The mapping of the initial boundary condition onto the final angular distribution has some special features. It is demonstrated that the Wannier mechanism does not necessarily imply a Gaussian distribution over the correlation angle.