DYNAMICS OF HE-3 IMPURITIES IN HE-4 FILMS

Using a microscopic theory we calculate the binding energy of He-3 imp urities in films of He-4 absorbed to a graphite substrate. Without adj ustable parameters, we obtain excellent agreement with the experimenta l binding energies for the ground state of the 3He impurity. By introd ucing a time-dependent variational wave function, the impurity atom ac quires a hydrodynamic effective mass for its motion parallel to the su rface due to hydrodynamic backflow, and the excited states have a fini te lifetime. When these effects are included, both the energy of the f irst excited state of the impurity, and the effective mass of the grou nd state, agree well with experimental data. A comparison with recent density functional results is carried out. It is shown that the substr ate bound states on strong potentials are spurious and due to the inap propriate treatment of the effective mass within that theory.