B. Helffer et H. Siedentop, A GENERALIZATION OF THE KUSTAANHEIMO-STIEFEL TRANSFORM FOR 2-CENTER SYSTEMS, Bulletin of the London Mathematical Society, 28, 1996, pp. 33-42
We generalize the Kustaanheimo-Stiefel transform to be applicable to t
wo-centre problems. As a consequence, we remark that-as in the one-cen
tre situation-the number of bound states below a given negative energy
E can be determined, under the usual assumptions on the absence of pe
riodic orbits, up to second order.