The diffusion Monte Carlo technique is used to calculate and analyze the excitation spectrum of a single 3He atom bound to a cluster with N 4He atoms, with the aim of establishing the most adequate filling ordering of single-fermion orbits to the mixed clusters with a large number of 3He 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.
Fantoni S. Guardiola Barcena, Rafael Navarro Faus, Jesús 2004 Excitation spectra of a He-3 impurity on He-4 clusters Physical Review A 70 2 023206
