Novel low-energy vibrational states of foreign particles in fluid 4He clusters

Novel quantum states of a foreign particle (M) within a fluid 4He cluster are proposed. The rovibrational states of M are considered to be similar to those of a particle in a box where the particle M can move nearly unimpeded in the fluid medium and the cluster surface provides the box walls. The energy levels are predicted to lie below those of the collective excitation states of the 4He cluster. The interaction between the box states and the collective excitations in the cluster is analyzed. The possibilities of detecting these new states in infrared spectra are discussed.