Spectroscopy of single molecules and clusters in helium nanodroplets. Microscopic manifestation of 4He superfluidity

Using recently developed techniques for producing beams of superfluid helium nanodroplets and for embedding single molecules or unstable particles (clusters and radicals) in such droplets, the spectra of molecules and clusters in a new type of a soft quantum matrix - liquid superfluid helium - can be studied. Methods for producing and studying helium nanodroplets in molecular beams, methods for embedding single molecules and clusters into droplets and spectroscopy techniques for single molecules and clusters inside helium nanodroplets. It is shown that based on spectroscopic measurements, the properties of helium nanodroplets themselves can be studied. Some properties of helium nanodroplets and trapped Bose-Einstein condensates are compared