ULTRALOW ENERGY SCATTERING OF A HE ATOM OFF A HE DIMER

We present a mathematically rigorous method suitable for bound-state a nd scattering process calculations for various three-atomic or molecul ar systems where the underlying forces are of a hard-core nature. We e mployed this method to calculate the binding energies and the ultra-lo w-energy scattering phase shifts below as well as above the breakup th reshold for the three-He-atom system. The method has proved to be high ly successful and suitable for solving the three-body bound-state and scattering problem in configuration space and thus it paves the way to study various three-atomic systems, and to calculate important quanti ties such as the cross sections, recombination rates, etc.