QUANTUM MANIFESTATIONS OF BIFURCATIONS OF CLASSICAL ORBITS - AN EXACTLY SOLVABLE MODEL

We examine photodetachment of H- in parallel electric and magnetic fie lds, h nu + H- --> H + e(-) using semiclassical approximations. The fi elds cause the electron to return to the atom, producing recurrences t hat are visible as interference oscillations in the photodetachment cr oss section. As the energy is varied, new returning orbits are created through bifurcations. Each such new recurrence increases the complexi ty of the absorption spectrum, and each bifurcation causes a local fai lure of the semiclassical approximation. The failure is repaired by a Fresnel diffraction integral.