  High resolution spectroscopy of doped molecules in 4He nano-droplets and
clusters gives a signature of superfluidity in microscopic system, termed as
microscopic superfluidity. Ro-vibrational spectrum of 4HeN-M clusters is
studied with the help of some important observations, revealed from experiments
(viz., localised and orderly arrangement of 4He atoms, although, being free to
move in the order of their locations; individual 4He atoms can not be tagged as
normal/ superfluid, etc.) and other factors (e.g., consideration that the 4He
atoms which happen to fall in the plane of rotation of a molecule, render a
equipotential ring and thus, do not take part in rotation; etc.) which effect
the rotational and vibrational spectrum of the system. This helps us in
successfully explaining the experimental findings which state that the
rotational spectrum of clusters have sharp peaks (indicating that the molecule
rotates like a free rotor) and moment of inertia and vibrational frequency
shift have a non-trivial dependence on N.
