SMALL-ENERGY 3-BODY SYSTEMS .5. THRESHOLD LAWS WHEN WANNIER THEORY FAILS

We investigate cases of Coulombic systems near the break-up threshold for which the Wannier model holds, but not Wannier theory. Making use of the classical trajectory method, we derive threshold laws for a mod el system of fractional charge (Z = 1/4 au) nucleus and electrons, and a real (though perhaps impractical) system of two beryllium nuclei an d an antiproton. For the first system we find the threshold law of the form exp (-lambda/square-root E), where E is the total energy, and fo r the second one a number of characteristic features above the classic al threshold have been obtained. Finally we investigate numerically a realistic case of an electron and two beryllium nuclei and discuss som e general features of the ionization probability above the classical t hreshold.