7 Ja n 20 04 Excitation spectra of a 3 He impurity on 4 He clusters

The diffusion Monte Carlo technique is used to calculate and analyze the excitation spectrum of a single He atom bound to a cluster with N He atoms, with the aim of establishing the most adequate filling ordering of single-fermion orbits to the mixed clusters with a large number of He atoms. The resulting ordering looks like the rotational spectrum of a diatomic molecule, being classified only by the angular momentum of the level, although vibrational-like excitations appear at higher energies for sufficiently large N .